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and that the materials composing granite were once in a melted state.

The igneous origin of granite is satisfactorily proved, from the phenomena of its veins;-from the calorific effects of these veins on the walls of the rocks, through which they have protruded;-from the intrusion of granitic matter between the strata of various rocks through which such veins have been forced, and lastly from the passage of known igneous rocks into granite.

The igneous origin of trap rocks has long been acknowledged by all competent geologists, but the general agreement that granite had the same origin is only of recent date. The proofs however of the origin of both are nearly the same.

Under the 66

Origin and phenomena of Trap Rocks," it will be seen that dikes or veins of basalt often protrude through the strata of other rocks, and that where they come into contact with these strata, the effects of heat are always apparent. The illustrations by diagrams, also prove that these veins, or dikes were forced through the fissures, or spread between the strata of the rocks, while the former was in a soft or semifluid state. The same phenomena are found to attend veins of granite which traverse other rocks, there being every indication that these veins were forced up from below in an ignited and softened state.

Fig. 16

The diagram Fig. 16, will show the manner in which granite sometimes traverses stratified rocks. This drawing is from Dr. Macculloch's representation of granite veins passing through gneiss at cape Wrath in Scotland. These veins it may be observed intersect each other in various directions, and are curious

ly branched and contorted. The mass of granite below the stratified gneiss, is also apparent, and as the veins end before reaching the surface of the gneiss, we cannot but in

fer that they were forced up in a softened state from the underlying granite with which their trunks are incorporated. Similar instances, that is, of granite veins traversing stratified rocks, and also rocks of granite, are known to occur frequently and in various parts of the world. In Europe such cases were formerly considered singular and important phenomena, and as they went to prove the igneous origin of granite, they were described with great prolixity and exactness. But the progress of observation has shown that granitic veins are quite common, and that particularly in mica slate, examples may be seen in almost any place, where circumstances allow the rock to be examined a few yards below the surface, and often on the surface itself.

In this country, Prof. Hitchcock of Amherst College, in his Report of the Geology of Massachusetts, has described and figured many such cases; some of which we shall take the liberty of inserting at this place.

Fig. 17, (fig. 11, in Prof. Hitchcock's work,) represents a vein of granite protruding through strata of hornblende slate. It occurs at Ackworth, New Hampshire, and is a remarkable locality of beryls, rose quartz, and crystalized mica.

"As the traveller approaches this spot," says the author, "he will observe while several miles distant, a remarkable

conical half naked peak, chiefly of white granite, shooting up about 300 feet above the surrounding country. This is the hill represented below, (Fig. 17,) as seen on its northwestern side, along which the road passes. The prevailing rock in the vicinity is gneiss; but in this elevation it is chiefly hornblende slate, traversed by an enormous granite vein, a, and exhibiting at least two protruding masses, b, and c, of granite. The vein varies from one half, to four rods in thickness, and the mass b, is four or five rods across: c, is only ten feet wide. The general direction of the lamina of the slate is north and south, and the dip from 15° to 20° east: but we have here the most decisive marks of its having been irregularly upheaved, and disturbed by the protruding granite. Near the foot of the hill, the slate is bent upwards, so that the chord of the curve is several rods long. But it is a curious fact, that the axis of the elevating force seems not to have coincided with the direction in which the vein was erupted. For the highest point of the curve of elevation, near the foot of the hill, is to the right of the vein at h; and as we ascend the hill we find the slate curved upwards near the vein more and more, as is shown by the drawing. Indeed the granite of the vein seems to lie on the elevated edges of the slate; so that the lower side of the vein dips northeasterly; and does not cut the slate perpendicularly. These facts would seem to evince, that the vein made its way through the slate, not along the line of the greatest pressure, but on the north side of it; probably because there the slate yielded most readily. We may suppose the melted granite below to have gradually elevated the slate, until at length it burst its way laterally through the rock. Such cases, I believe do sometimes occur in existing volcanoes.

"The masses of granite b, and c, are probably other examples in which the molten matter burst its way laterally through the slate. And it is an interesting fact in regard to the mass b, that in some places it still projects over the slate several feet, forming in fact an overlaying mass. stances of this kind I have rarely met with in the granite of New England." Page 480.

In

Fig. 18, also from Prof. Hitchcock's work, represents a nearly perpendicular ledge of mica slate in Conway, Mass. The strata as shown by the drawing, are much contorted, indicating disturbance during their deposition, or while they were in a soft and yielding state. a, a, are strata of com

mon mica-slate: b, is a stratum of amphibolic slate. The whole surface exhibited is fifteen feet long and eight feet high. Through this ledge runs a vein of fine grained granite a foot wide.

"The object of giving this sketch" says Prof. Hitchcock, "is to show that this vein has produced no derangement of the mica-slate: for the different particles of that rock occupy the same relative position on the different sides of the vein. Hence the vein was introduced subsequently to the consolidation of the slate; and probably it was injected into an open fissure."

Dr. Hibbert describes the manner in which granite has gradually passed into basalt in one of the Shetland Islands. The basalt extends from the island of Mickle Voe, northwards to Roeness Voe, a distance of twelve miles. On the west of this there is a considerable mass of granite, and the transition from the one into the other is thus described. "Not far from the junction we may find, dispersed through the basalt, many minute particles of quartz. This is the first indication of an approaching change in the nature of the rock. In again tracing it still nearer the granite, we find the particles of quartz dispersed through the basalt becoming still more numerous, and larger, an increase of magnitude even extending to every other description of particles. The rock may now be observed

to consist of separate ingredients, of quartz, of hornblende, felspar, and greenstone; the latter substance, (greenstone,) being a homogenous commixture of hornblende and fel spar. Again as we approach still nearer the granite, the disseminated portions of greenstone disappear, their place being supplied by an additional quantity of felspar and quartz. The rock now consists of three ingredients, felspar, quartz, and hornblende. The last change which takes place, results from the still increasing accumulation of quartz and felspar, and from the proportionate dissemination of hornblende. The hornblende eventually disappears, and we have a well characterized granite, consisting of two ingredients, felspar and quartz." Ed. Journal of Science, vol. i. p. 107.

We see from these examples, that granite has been forced from below into the fissures of other rocks which were superincumbent, consequently, which were deposited after the granite was formed. In several instances it may be observed also, that the granite does not reach the surface, by which it is proved that these veins could not have entered from above, a theory long maintained by those who claimed that granite was of aqueous origin. Besides, the indications of fusion which these veins present, the passage of granite into basalt, a rock which all agree bears the marks of fire, is additional evidence that they had a common origin.

But if we consider granite veins to have forced their way from below, in a state of igneous fusion, then we might expect, that when the mass came into contact with stratified rocks, the strata would be separated, and that the fluid matter would run between them, at least to a short distance, and especially near the surface, where the pressure would present little resistance to the separation of the strata. Now this is precisely what is known to have happened in numerous instances, one of the most striking examples of which occurs at Glen Tilt, in the Grampian mountains in Scotland.

At this place, veins of red granite are seen branching out on the northern side of the glen, from the principal mass, and meeting the slate and limestone which forms the southern side. The granite veins run in all directions, intermingling with, and disturbing the strata of the other rocks, in such a manner as to prove, not only that the granite was in a fluid state at the time of its intrusion, but also, that it was forced up with great violence.