not by great rushes. But they could not assume that it would always do so, and must prepare for the occurrence of a great rush. The true character of lightning must be discovered by observing lightning, and not by experiments in a laboratory. The spark of one induction-coil at a considerable distance would start another one sparking merely by its light. From that he came to the conclusion that when there was a very bright flash of lightning, it must involve very important con sequences. There was no doubt that it would cause discharges all over the neighbouring area, and so he would say that areas of protection were misleading, and if a flash had that effect, they had better be without it if possible.

It

The Hon. Ralph Abercromby, who showed a number of photographs of lightning flashes, said there was no absolute evidence in the photographs of flashes of lightning following each other rapidly on exactly the same path. There was, however, distinct evidence of the tendency of lightning-flashes to occur parallel to each other. There seemed to be a tendency in lightning flashes to be ramified, to give off threads all round the main flash. Photography gave conclusive evidence that flashes were not so instantaneous as was generally supposed. showed that the flash did not always jump from a cloud straight to the earth, but sometimes went meandering through the air and tying itself into knots, so that it could not be so instantaneous as was imagined. He was of opinion that lightning-clouds were generally more than 500 feet high, but lightning was rarely much higher than 10,000 feet high. By this he did not mean that lightning might jump 10,000 feet from the cloud to the earth; but that at an altitude of 10,000 feet on a mountain-side a thunderstorm was usually below the observer.

Lord Rayleigh said that, although some mathematicians were unpractical, yet it was to mathematics one must go to find the results of known causes under new circumstances. He had no special knowledge of lightning-conductors, but from his general acquaintance with electricity he should say that Prof. Lodge's experiments could hardly fail to have a most important practical application to lightning-conductors in the future. Mr. Preece spoke of the development of energy by the condensation of vapour into water, but the question was to find how some of that energy came to take the electrical form.

It

Sir W. Thomson said that mathematicians never predicted that the Atlantic cable could not be laid, but a celebrated engineer did so. He thought Prof. Lodge was in the American stage of inertia and Mr. Preece in the English stage. He believed that if Prof. Lodge proceeded with his experiments he would confirm his discovery that iron wire was a better conductor than copper. Self-induction was in the air, and they were talking of nothing else. He thought Mr. Abercromby's idea as to the duration was correct. seemed to him probable that it was the sound of one spark which caused another rather than the light. There was the photograph giving three parallel flashes. It would be well if some experiments could be made to discover whether flashes occurring like that were simultaneous or followed one another, being started by the light or sound vibrations of the first. was rather startling to find that a lightning-rod had protecting power over so small an area, and he would like to ask Mr. Preece whether copper had been experimentally proved to be better than iron. They could come to one conclusion from what they heard-namely, that houses made of sheet iron would be the safest possible places in a thunderstorm. The question of the effect of self-induction on statical discharges was a very important one. He suggested as a class experiment the discharge of a Leyden jar through a number of students (1) when they were arranged in zigzag rows, so as to have no self-induction in the path of the discharge; and (2) when they stood in a circle, so that the self-induction of the path was a maximum. The students should stand on insulating material. He thought the result of such an experiment would be to show that the students in the middle of the chain would feel the effect of the discharge far less in the second instance than in the first. With reference to the reports as to the occurrence of globular lightning, he believed them to be much exaggerated, and expressed an opinion that the whole effect might be a physiological optical delusion. Reiss experimented some forty years ago on the question of magnetism by jar discharges, and found that the direction of superficial magnetization sometimes was the one to be expected, sometimes the opposite one. He suggested new experiments as to the influence of the rate of oscillation on the result. mcst efficient protection for gunpowder against lightning would

The

be, he thought, to put it in a house whose exterior was entirely of iron and to put no lightning-rod on it.

Prof. Rowland observed that the conditions of Prof. Lodge's experiments were scarcely the same as those of actual lightning, and he pointed out that the length of the spark was no measure of the resistance of the conductor. Further, he showed some effects in Mr. Abercromby's photographs which were probably due to the astigmatism in the lens of the camera.

M. de Fonvielle, who spoke in French, observed that Sir William Thomson had said most eloquently that Mr. Preece was taking the English side of the question and Mr. Lodge the American side, but he must say that Sir William Thomson himself had taken the French side, and he had proposed a revolutionary system which consisted in the building of iron houses. He took the liberty, though being a Frenchman, to disagree with the great electrician, and to stand with Mr. Preece as an English conservative, with reference to lightning conductors. Lord Rayleigh said that mathematicians and physicists should unite together, but he supposed that Lord Rayleigh would agree with him in remarking that Mr. Preece was realizing that alliance in a very remarkable manner, for on the one hand he dealt with a large number of experiments and observations of natural facts, and on the other hand he introduced statistics, or rather the calculation of probabilities, which was one of the highest branches of mathematics. The experiments made in laboratories were different from those which were presented by Nature only so far as they were conducted on very widely different scales. On the previous day, in that hall, M. Janssen had proved by his observations on the action of oxygen on the composition of the electric light that in many phenomena there was a coefficient behind. He congratulated them on the aid they were now receiving from photography. He should advise the meeting to delay its opinion for the time until the completion in Paris of the Eiffel Tower, which would be the most extracrdinary lightning-conductor in existence, being 1000 feet high. He must, moreover, state that Paris was practically free from calamities produced by lightning. They had erected a sufficient number of lightning-rods, according to the principles so admirably advocated by Mr. Preece, and that was a strong evidence that Mr. Preece was altogether travelling in the right direction, quite irrespective of any mathematical or physical demonstration. Prof. George Forbes said that Mr. Preece did not mean to say that mathematicians came to wrong conclusions when they had all the right data, but that they sometimes came to a conclusion without taking all the data into consideration. Prof. Lodge had come to say that if iron was not better than copper, it was at least as good; but they could not be quite prepared to accept that, because the experiments might be tried in instances more nearly approaching the natural conditions, and in that case it was quite possible that copper would be found to be the best.

Sir J. Douglass said that his experience of lighthouses protected by lightning-rods covered a space of forty years, and was comforting to the members of the Lightning-Rod Committee. He never knew a rod fulfilling the conditions he prescribed to fail in protecting the lighthouse and adjoining buildings.

Mr. J. Brown suggested the use of a revolving camera in taking photographs, in order to separate flashes, and thus see if cach is single or not.

Mr. Sidney Walker said that anything which would cheapen lightning conductors would be gladly welcomed. In the cases where damage had occurred, he believed that the result was due to a defect in the conductor. He pointed out that iron would not stand the weather so well as copper, and that, besides, it would be affected by the gases at the top of a factory or similar place.

Mr. G. J. Symons said he had investigated every accident by lightning of which he could hear, and had so got valuable experience. The conclusion left on his mind was that if people would erect conductors precisely in accordance with the rules laid down by the Conference, and fulfilling all the conditions, they would be absolutely safe. Where accidents occurred to buildings with conductors, there was a reasonable explanation to be found. Prof. Lodge's experiments were laboratory experiments, and to get the real facts they must have something on a much larger scale, perhaps by a series of interrupted conductors on posts on the tops of some of those high hills where storms frequently occurred. With regard to protected areas, there were only two cases on record, and those doubtful, of anything being struck within a protected area.

1 Report of the Lightning-Rod Conference (Spon, 1882).

Dr. Walker said he saw an obelisk on top of a hill struck. The top was knocked off, and the fluid came from the steps of the monument at fourteen different points, ploughing up the ground, and breaking rock at 100 feet distance.

Mr. Wood thought the black flash shown in one of the photographs was due to the reflection of one of the other flashes.

Lord Rayleigh said Stokes attributed that to the combination of gases in the path of the flash causing an opaque stratum.

Prof. Lodge said he could not understand why a conductor should have such a good earth. Why did not three points do at the bottom as well as at the top? If properly constructed conductors never failed, how was it that the hotel at Brussels was burnt, for that was considered protected in the most orthodox way? He would not say that conductors were of no use; they were of great use, but not absolutely certain. In his experiment he was bound to adopt the plan he did, because the experiments could not be done in any other way. It was only the outer surface of the conductor which conducted, and there was no particular good in the centre of a rod. A tube would do as well, and would be all the better if opened out into a flat bar, and yet better than that would be a strand of wires. Iron buildings, to be safe, must have perfect connections, for the smallest gap might give off a spark. That was the danger in houses supplied with gas; if the fluid travelled along the pipes and came to a gap, a spark and a fire might result.

Mr. Preece said the points between Prof. Lodge and himself were reduced to a very small compass indeed. He himself had always been a great advocate of iron on account of its cheapness. The use of copper caused needless expense in the erection of lightning-conductors. He believed every private house could be protected in accordance with the recommendations of the Conference for £1, if people would buy a coil of stranded iron wire a quarter of an inch in diameter, with the finial points, and have that put up.

The President summed up the discussion, and said the principal thing for them to pay attention to was that prevention was better than cure. There could be very little doubt that the presence of a considerable number of conductors afforded a great deal of protection to the area in which it existed, as was shown in the instance of Paris. It was desirable, if possible, that the whole country should be covered with conductors to prevent the discharge of flashes. There was no doubt that, though there might be room for improvement in the conductors, they had on the whole been right.

THE INTERNATIONAL GEOLOGICAL

CONGRESS. II.

IN order to understand the present status of the Congress, and to forecast its probable future, we must briefly note the work done at the two preceding meetings, and compare that with the general results of the meeting just closed. At Bologna the greater part of the time was occupied with discussions upon the exact meanings to be attached to various geological terms, and upon the general principles which should guide us in geological classification. Certain rules were then laid down, which probably few authors have consistently followed, and which it is unlikely will be universally adopted. At Berlin the discussions turned more upon precise questions of classification, especially those relating to the sedimentary rocks; upon the lines by which various groups of strata should be marked off; and, in some cases, upon the names by which these groups should be known. This change of procedure was necessitated by the progress made with the international geological map of Europe; the material for such discussion on classification having been provided in the shape of Reports from various national Committees, of which that from England, presented by Prof. Hughes, was by far the most complete.

At the London meeting the classification of the Cambrian and Silurian strata was fully discussed; and two other questions, only lightly touched upon before, were here

1 Continued from p. 526.

considered in some detail-the nature and origin of the crystalline schists, and the upper limit of the Tertiary system.

In Bologna numerous votes were taken, in Berlin several, but in London none The English geologists were in a majority sufficiently large to carry any point upon which they were fairly well agreed, but no attempt was made to test this; and Prof. de Lapparent, in presenting a Report from the Committee appointed by the Council to consider the question of voting, paid a generous tribute to the English members for their self-restraint. There can be no doubt that the adoption of this Report marks an important epoch in the history of the Congress, and that resolutions hereafter voted will carry more weight than those which at present stand on its records. It recommended that members of the country in which the Congress meets should vote separately from the foreign geologists if the votes of the two groups agree, the question will be taken as settled; if they disagree, the further consideration of the question will be postponed. The resolution further recommended that votes should not be taken on questions which are purely theoretical-such questions to be simply discussed, and various views obtained; and that decisions of the Congress should only refer to the more practical questions.

Two Commissions of the Congress have existed since the Bologna meeting-that on the Map of Europe, and that on Nomenclature and Classification. The work of the former is plainly marked out, and much has yet to be done. The other Commission has, however, in many respects served its purpose; it has obtained Reports from the various national Committees, most of which have been ably summarized by Prof. Dewalque. The future work of the Congress will partly lie in discussing these Reports, and in deciding such questions in general classification as may apply to wide districts, leaving minor points to be worked out by each country for itself. A Commission was therefore appointed with altered and somewhat wider powers; its functions will more fully shape themselves at the Congress in Philadelphia. As the future progress of the Geological Congress lies so much in the hands of this Commission, it may be desirable to record here the names of its members, which are to some extent the same as those already given (p. 519) for the Council of the London meeting, but there are some additions and changes:-Germany, Zittel; Australia, Liversidge; Austria, Neumayr; Belgium, Dewalque; Bulgaria, Zlatoski; Canada, R. Bell; Denmark, Johnstrup; Spain, Vilanova ; United States, Hall; Szabó, India, Blanford; Italy, Capellini; Mexico, CasFrance, de Lapparent; Great Britain, Hughes; Hungary, tillo; Norway, Kjerulf; Netherlands, Calker; Portugal, Delgado; Argentine Republic, Brackenbusch; Roumania, Stefanescu; Russia, Inostranzeff; Sweden, Torell; Switzerland, Renevier. Prof. Capellini was elected President of the Commission; and Prof. Dewalque, Secretary.

The Report upon the Map of Europe was presented to the Congress by Dr. W. Hauchecorne. This stated the progress which is being made. Four or five sheets of Central Europe will be ready for publication during the next two completed, each with its own title and index, instead of years, and it has been decided to publish the sheets as waiting for the completion of the whole of Europe, as was at first intended. A proof sheet (C iv.), containing a large part of Northern Germany, was exhibited; on this there are twenty-four different tints for the sedimentary formations, three for the Archæan, and nine for the eruptive rocks. The map is on the scale of I: 1,500,000, and will consist of forty-nine sheets. One colour is taken for each great group-Cretaceous, green; Jurassic, blue; &c. The subdivisions are shown by various modifications of these colours. As a rule, the lower subdivisions are shown by the darker tints, so that the map may be read with more facility than is usually the case with geo

logical maps. The map of the British Isles was handed in for publication at the closing meeting. Very little time was given to the map in the public sessions of the Congress, but the Map Commission had three long sittings, the results of which will be printed in the official Report. The most important points arrived at were the adoption of the term Pleistocene for the index of the map (the German term 'quartär” to be bracketed with this); the separation of the modern deposits from the Pleistocene, and the mapping of the latter wherever practicable, the underlying formations (where known) to be distinguished by coloured lines; in modern eruptive rocks (those of volcanoes now active or only recently extinct) the stratified volcanic tuffs are to be distinguished from the cinders and the scoria.

66

M. Karpinski has been the representative of Russia on the Map Commission. On this occasion he was not present, his place being taken by MM. Nikitin and Tschernicheff. The latter submitted an important note on the crystalline schists of the Ural Mountains, which would have enlivened the discussion upon this question in the public meetings of the Congress. He states that the crystalline schists of the Urals contain limestones with a distinct hercynian fauna, and also that the schists pass horizontally into Devonian strata. It is probable that in cases of this kind (and similar cases elsewhere were referred to in the public discussion) the schists will be represented by the colour denoting their presumed age, whilst their present lithological character will be denoted by coloured lines. M. Nikitin raised a point which is important in many parts of Europe, but which is especially so in Russia-that is, the necessity of distinguishing transitionbeds. He instanced the Volgian beds, which link the Jurassic with the Cretaceous; the Tartarian, between the Permian and the Trias; and others, spoken of by M. Nikitin as Permo-Carboniferous, which link the Permian to the Carboniferous. These transition-beds occupy immense areas in Russia, and cannot well be fitted into the existing classification.

The discussion on the crystalline schists occupied the whole of the sitting on Wednesday, and part of that on Friday. The material for this discussion had been provided by a collection of papers printed in advance and distributed at the opening. Translations from parts of this polyglot pamphlet have now appeared in NATURE. Essays in English were also contributed by five officers of the United States Geological Survey, with an introduction by Major Powell; and by Mr. Lawson, of the Geological Survey of Canada. One by Reusch, on Norway, also in English, was received too late for printing in the pamphlet, but it will appear in the full Report of the Congress.

This discussion derived additional value from the fine collection of rocks, maps, lectures, &c., illustrating this particular subject close at hand in the temporary Museum. The Geological Survey exhibited a large collection of rocks, maps, sections, &c., illustrating the North-West, the Central, and the Southern Highlands of Scotland; important collections of British rocks were also exhibited by Bonney, Blake, Hicks, Callaway, Cole, Hatch, Rutley, Wunsch, and others; foreign rocks were exhibited by Bell from Canada, Delgado from Portugal, Torell from Sweden, Reusch from Norway, Giordano and Mattirolo from Italy; whilst maps, drawings, models, &c., illus trating the discussion, were exhibited by Teall, Baltzer, Cadell, Ricketts, Lapworth, and others. Special mention should be made of the splen lid colection exhibited by Heim, illustrating the deformation, crushing, &c., which the rocks of the Alps have undergone. All these exhibits are described in the Catalogue (54 pages with supplement of 4 pages). Several members of the Congress assisted in the arrangement of this Museum, but its success was chiefly due to the labours of Dr. Hinde, Mr. Teall, and Mr. Rudler.

In the foregoing notes we have not attempted to summarize the discussions. These were reported at

some length in the Times and in other papers. We have preferred to devote the space at our disposal to a general survey of the meeting, and to note some points of importance which could not well be included in a formal report of daily proceedings. As already stated, the discussions may by some be held to have led to no definite result, inasmuch as no vote was taken and therefore no formal decision of the Congress can in future be appealed to. But the great value of such meetings lies in the opportunity afforded for personal discussion and the interchange of opinions, not only in the public sessions, but in the more easy and informal conversations over the exhibits in the Museum, in the corridors and reading-room, and at the friendly and social gatherings which made so pleasant a feature of the London meeting. We have no doubt that the general result of this meeting on geological opinion and progress will be at least as good as that of any which has gone before.

The London Congress was particularly fortunate in its place of meeting. Within the walls of the University of London there was ample accommodation for all the requirements of the Congress, whilst close at hand were the Jermyn Street Museum and the rooms of the Geological Society. Unfortunately the Honorary President, Prof. Huxley, was kept away by ill-health; Prof. Hughes, who has done so much for the Congress in England, was also unable to attend. The early death of M. Fontannes, who has so ably reported the proceedings of previous meetings, is a great loss to the Congress, and many fears were expressed that his place could not be adequately filled; but the labours of Messrs. Hulke and Foster in the Council, and of Barrois and Renard at the meetings, resulted in fuller reports than have appeared of any previous Congress.

REMARKS ON SOME OF THE MORE RECENT PUBLICATIONS DEALING WITH THE CRYSTALLINE SCHISTS.1

IN acceding to the invitation of the Geological Congress to contribute to the discussion of the crystalline schists, the author expresses his regret that his time has not allowed him to throw new light by fresh observation on the points of controversy. Other labours have for a long time completely occupied him; so that he has only been able to occasionally assist with advice a younger fellow-worker, Herr Emil Danzig, of Rochlitz, in his researches on the Saxon granulites. This work, which has but recently been brought to a close, and has been placed at the disposition of the members of the Congress, is recommended to the notice of those fellow-workers who are

interested in these matters, for in it the granulite question has been completely treated and advanced another stage.

Prof. Lehmann still takes his stand on the results furnished him four years ago by his investigations on the old crystalline schists.

The, on the whole, favourable reception of those investigations assuredly indicates that the right path has been struck, and that an extension of our views on the crystalline schists has resulted from them. This is also proved by the fact that these views have also been successfully applied in other places. That in many cases the opinions advocated by the author have not been rendered quite correctly, cannot excite surprise. Such misconceptions were scarcely to be avoided.

Prof. Lehmann strenuously opposes the notion that his generalizations were made without due consideration, and draws attention to certain criticisms to which his work has been recently subjected.

Ás is well known, the controversy on the Saxon granulites turns on the question, whether their plainly developed parallel structure is to be regarded as true bedding in the sense of sedimentary deposition, or as of eruptive or plutonic origin. The same questions arise in the discussion of all other districts in which crystalline schists occur; the solution, however, will by no means always be the same. It is beyond doubt that a whole

"Bemerkungen zu einigen neueren Arbeiten über Krystallinischschiefrige Gesteine," by Prof. J. Lehmann. Published by the International Geological Congress, London, 1888. (Abstracted from the German by Dr. F. H. Hatch.)

series of crystalline schists are of sedimentary origin, and it is a matter to be decided by detailed investigation which are to be considered as sedimentary and which as eruptive or plutonic. The results obtained by the author in the investigation of the Saxon "Granulitgebirge" and some adjacent districts do not therefore claim universal application.

The tentative interpretations given by him were arrived at by the close ob ervation of the field-relations of the rocks in question during a geological survey extending over several years; and it can now only be a question in how far the interpretation, which has been recognized with certainty as correct for a series of phenomena, can be applied to other phenomena intimately related to them. The author admits that here and there he has gone somewhat too far in his tentative interpretation. It was scarcely possible, in so difficult a question as the " granulite question," which to-day has not yet reached its final limits, to go just so far that later experience should find nothing to modify. But the description of the author's work by J. Roth (in a paper on Zobtenite," read before the Berlin Akademie der Wissenschaften on June 23 of last year) as "a marvellous agglomeration of the most daring hypotheses" is scarcely justifiable.

In Prof. Lehmann's investigations on the crystalline schists it has, for the first time, been shown in the greatest detail that their present condition cannot be original, but must be one that has been influenced by the dynamic processes accompanying mountainbuilding. He is far from maintaining, however, that similar observations had not already been made; and he readily acknowledges that eminent investigators of the crystalline schists, such as Kjerulf and Michel-Lévy, had, at a much earlier period, made such observations. What is new is the -mode and method in which the author utilizes his observations. Researches of this kind were sunk into oblivion: the theory of the sedimentary origin of the crystalline schists had become the ruling dogma; and the Eozoon canadense had also made its appearance in Europe.

Roth, in the paper referred to, maintains his old position, according to which the crystalline schists, including the phyllites, are plutonic and unaltered formations.

The evidence advanced by him to prove that the stratiform gabbros, which he terms zobtenite, cannot be numbered with the eruptive rocks is insufficient. The occasional observation of conformable relations with other crystalline schists is inadequate. This does not, however, hinder Roth from regarding it as proved that the Zobten rock cannot be eruptive. The isolated patches of the old rocks that crop out in Silesia are unfortunately extremely confused. The stratigraphical relations of these rocks, which are very highly metamorphosed, cannot be utilized to support either view, and no hope is to be entertained of more favourable exposures in the future.

Prof. Lehmann's views on the Saxon granulites have, in the main, been confirmed by the before-mentioned work of Herr E. Danzig. This work again shows how confused are the fieldrelations in the granulite-district, and that few exposures permit of an indisputable solution.

In the northern half of the Saxon district the granulite assumes a granular structure, and acquires a marked similarity to some "bedded" granites. These points have received especial attention from Herr E. Danzig. He comes to the conclusion that in many places no sharp line can be drawn between granulite and granite; further, that rocks, which belong undoubtedly to the granulites, present, like the granitic gneisses occurring in the granulite-complex and interbedded with mica-schists, the character of eruptive masses. They contain included fragments, and impregnate these as well as their immediate neighbourhood. The supposition formulated by Prof. Lehmann at the close of his researches in this district is thus confirmed-namely, that the Saxon granulite is a granite massif, which has been influenced in structure and composition by dynamic metamorphism.

This confirmation of his work induces the author to explain why he cannot accept the views advocated by E. Reyer in his newly-published work on "Theoretical Geology." Reyer holds the Saxon granulite-massif for "a mass of eruptive granite AMassenerguss), mantled over by tuffogenic sediments (granulite), through which granite dykes are extruded from the central mass; while granite sheets (Flanken-rgüsse) are intercalated between its beds." Reyer might have gathered from the author's work that the Saxon granulites are, in the main, by no means highly metamorphosed: on the contrary, they deviate very little, in part not at all, from the original structure of eruptive granite rocks.

But apart from this, and without dwelling on the fact that we know absolutely nothing of the rocks underlying the Saxon granulites, the supposition that the alternation of mica-schists with granulite or granitic gneisses has been produced by an accumulation of successive lateral eruptions (Flankenergüsse) and precipitated sediments, cannot hold good.

The theoretical considerations of Reyer, the utility of which is gladly recognized by the author, and which in many cases can be supported by direct observation, must not be allowed to prejudice our judgment. The actual facts must first be estab lished, and in so doing we do not encounter the streaky and platy structures which characterize the direction of movement in magmas. We see, in truth, something quite different. The bedded" granite presents no zones of consolidation that follow closely the surrounding slates; we see rather an extraordinarily uniform mass of granite at first traversing, in a dykelike manner, the slates, but afterwards insinuating itself between them, in both cases enclosing fragments of the traver: ed rock. Where the granite was intruded as a dyke these fragments lie without order, but where it forms a sheet the flat pieces are, almost without exception, arranged parallel to the walls of the dyke. We are accustomed to regard granite, occurring as a dyke, as younger than the rock in which was formed the crack along which the molten rock ascended, without wishing to deny that it has existed, from the very beginning, deeply hidden in the bowels of the earth, and is therefore, in reality, older than the slates it traverses. But it has become customary to observe the convention; indeed, it is necessary to do so if we do not wish to be involved in universal chaos.

For the "bedded" granite it is no simple matter to prove that it is younger than its hanging wall. Attentive examination shows that the apparently conformable boundary has no such very conformable course; that, further, the apparently sedimentary beds are sometimes distinctly detached, and turn out to be loose masses; finally, a whole series of detailed phenomena show that wherever there have been dislocations, the granite has followed the opening and has impregnated the slates. How far such an impregnation can be assumed to have taken place is a matter for personal experience.

In the granite dykes the inclusions and the boundary surfaces of the slates present exactly the same phenomena; only in this case the fragments do not all present a parallel arrangement.

One would be driven to deny the possibility of strata or slatemasses being split parallel to their stratification or their bedding, if we were to deny that the "bedded" granites do not as much constitute a case of intrusion along cracks as do the obliquelyrunning granite dykes. Why should there not be, among such a number of granite dykes that run unconformably, some that have been formed by the in filling of cracks (of seldom more than 400 metres width) that follow the divisional planes of strati fication or cleavage? It is not to be supposed that these were cavities, the wide sweeping arches of which were supported by the rigidity of the lateral rock-masses: as fast as the slates were separated the granite forced in its way, and filled up the crack as soon as it was developed.

This separation along parallel divisional planes and intimate impregnation with eruptive material, which can be followed in the minutest details with the greatest clearness, arouse the question as to whether the same phenomena have assumed greater dimensions-dimensions that would still be trivial in comparison with the masses erupted. The author has described several exposures in the Saxon granulite district that render any other interpretation impossible.

Kjerulf, Michel Lévy, and others have described very similar relations among eruptive masses. Michel Lévy has quite recently given expression to his opinions in a "Note sur l'origine des terrains cristallins primitifs," and in a "Note sur les roches éruptives et cristallines des montagnes du Lyonnais." His statement to the effect that the author and a portion of the German school assume a development of heat by the plication of the earth's crust is, so far as the author, is concerned, incorrect. On the contrary, he has shown that a conversion of motion into heat has left ro visible traces. He is quite at one with the French investigator as to the origin of the heat in the earth's

crust.

The chief requisite in the discussion of the crystalline schists, is never to leave the solid ground of facts, and to pay particular attention to the collecting of these. If the statements of some authors are examined, it must awake astonishment to see with what positiveness statements are made, which, although of the

greatest importance for the proper judgment of the genesis of rocks, do not correspond in the least to the facts, and by a little attention might easily have been avoided. The author has already had occasion to disprove the non-occurrence of fragments of clay-slate in the phyllite-gneiss of Goldkronach in the Fichtelgebirge, as maintained by Gumbel. A few hours' search sufficed to collect the clearest examples of abruptly fractured and injected enclosures From this occurrence Gumbel drew widely generalized conclusions. Whether it is enclosed fragments or concretions that are contained by a rock, is assuredly of the greatest importance for its proper explication.

The author then refers to the Ober-Mittweida conglomerate. Roth has described the pebble-like fragments enclosed in this rock, as concretions. The author cannot agree with him in this determination, and gives his reasons, which are mainly based on petrographical considerations, why he does not do so.

It will hardly be denied that dynamic processes involved in mountain-building, be the latter referred to whatever cause one will, have not only not been without influence on the structure of the rocks already in existence, but have also considerably influenced the distribution and the intrusion of the eruptive mas es. The observations which the author has published on the gabbros of the Saxon granulite district, on banded granulites, on the conglomerates of the Saxon Erzgebirge that have been metamorphosed to mica-schists, and on Bavarian "Pfahlschiefer," have not been refuted, although their reexamination would not have been attended by any especial difficulties.

The author then concludes by expressing the wish, that, in the further study of the crystalline schists, metamorphosed sediments, which can, it is true, be altered to true mica-schists, but never to true gneisses of uniform structure, should be kept distinct from those mica-schists of which we do not know the origin, and from the true granitic gneisses. If this be not done, the false conclusion is inevitable that sediments pass through mica-schists into gneisses. Metamorphosed, gneiss-like sediments, in which allothigenic minerals like feldspar are associated with authigenic quartz and mica, and which are, to the author's mind incorrectly, often designated gneiss, should be described as gneissose greywacke, or as gneiss-greywacke. Some such divisional line must be drawn if we are to obtain any enlightenment on the structure and origin of districts composed of crystalline schists and massive rocks. Dubious schists should be represented by a neutral colour, and not lumped in with the gneisses. The designation gneiss is meaningless as long as the most diversified crystalline and semi-crystalline schists are included under it.

Gneisses, to the author's mind, are granites possessing a parallel structure, which is partly original, partly the result of a more or less intense pressure during, or subsequent to, consolidation. Whatever else may be said, gneisses and granites are things that belong to the same category, and the author cannot reconcile himself to their separation, with respect to origin.

It cannot be natural to arrange in separate petrological categories eruptive granites and non-eruptive granites (gneisses), eruptive diorites and non-eruptive diorites, eruptive gabbros and non-eruptive gabbros, and to treat them from distinct points of view. Plutonic rocks do not differ from the similarly composed eruptive rocks, because they have not left the place in which they were formed.

How the origin of the plutonic rocks is to be conceivedwhether as the primordial terrestrial crust, or as produced by the melting down or diagenesis of sediments, the latter supposition involving logically a similar origin for a part, at least, of the eruptive rocks-are questions of which the answers are at present less pressing, and which, with certitude, we shall probably

never solve.

Dip of strata, 12° to 15° N. All strata unaltered and undisturbed.

The above section proves that in North America, as in Sweden, the Olenellus fauna is beneath the Paradoxides fauna. This changes the American scheme of classification of the Cambrian system, and places it in harmony with that of Europe. The Olenellus fauna in America includes 42 genera and 112 species, and I now recall 4 genera and 20 species from Europe not known in America, which give a fauna of 46 genera and 132 species beneath the Paradoxides zone.

The following table exhibits the succession of the terranes as now known in America :

THE STRATIGRAPHICAL SUCCESSION OF THE CAMBRIAN FAUNAS IN NORTH AMERICA.

A REVIEW of the opinion of American geologists on the succession of the Cambrian faunas shows that all have followed the scheme published by Sir William Logan in 1855

Abstract of remarks made by Chas. B. Walcott, of the United States Geological Survey, before the meeting of the International Geological Congress in London, in the course of discussion on the Cambrian System, on September 18, 1888.