In treating of mountains, I have mentioned their usual direction as being frequently the same. The parallelism of beds, called also Loxodromism, is very surprising. The primary beds on the coast of Genoa, the plains of Lombardy-the Alps of St. Gothard-Swabia and the north of Germany, were first noticed by Humboldt to run almost constantly from south west to north east-and this was one of the reasons that led him to South Ame'rica, where he noticed the same in the chain of mountains running from the lower Oronoko to the basin of the Rio Nigro, and the Amazon. This Loxodromism has already been mentioned in speaking of the uniform direction of mountains from north east to south west. This is the direction of our Allegany Mountains, one of our most interesting geological features. From the sources of the St. John River, New Brunswick, it runs south west to the junction of the Alabama and Tombigbee Rivers. At the distance of from 40 to 80 miles it follows and skirts the Atlantic, forming a mighty barrier to a mighty ocean. Granite, gneiss, and micaceous schist, each form a considerable part of this immense ridge. Granite is found on the tops of mountains and on plains, and is frequently so decomposed as to have lost adhesion for 50 or 100 feet below the surface, exhibiting only sand and gravel. Gneiss is more widely distributed-and covers nearly half of the primary ridge, including immense beds of granite, some of them 300 feet thick; in which beds are found the Emerald, Tourmaline, Garnet, &c. Micaceous Schist and Argillite are also widely distributed. Primary Mountains may be said generally to be unfavorable to vegitation: their extreme hardness, their precipices, and unfriendly soil, doom them to barrenness. Lichens and mosses attached to their sides decay, and furnish soil for larger plants-Water penetrates and breaks off masses— the influence of air, water, heat and light assist in the progress of disintegration-and insensibly, but uniformly and constantly, aid in converting stones into bread-or, in other words, in preparing soil from the most sterile rocks for the support of animal and vegitable life. The decomposition of granite is slow, and when decomposed the unfriendly siliceous grains are easily washed away. There is neither vegitable nor animal matter in the compound; it does not absorb moisture, letting the water percolate ;-nor does it retain heat. The soil made from gneiss is not washed away quite so easily-and the mica yields it more argillaceous earth-but it is seldom deep (from 20 to 100 feet.) Micaceous Schist and Argillite decompose more rapidly, and form a better though not a good soil. The rivers of primary districts have rocky beds and precipitous banks. Upon the whole, Primary Mountains are covered with a soil less productive than the other classes of rocks-and form the barren regions of the Arctic, and the sterile plains of the Torrid. To compensate, in some degree, their water is more pure and clear, and the inhabitants more healthy. LECTURE VI. Transition Rocks--Argillite-Greywacke—Lime stone--Gypsum--Porphyry-Sienite-Greenstone.— Alluvia-Diluvia Resting on the Primary Rocks already described, we find others, that have been denominated by Werner, Transition, by others, the Intermediate, the Medial, the Sub Medial, and by Hutton, the Stratified. They never attain the elevation of the preceding rocks, and are more liable to decomposition. They are considered as not crystalline. They are the oldest or lowest rocks in which we find any record of vegitable or animal existence, and may be regarded as ancient re cords, imprinted with the natural history of the inhabitants of the globe. They repose on the primary class, and form a contrast to their bold precipices and rugged peaks, by their less pointed, and more beautiful outline. In retaining the term Transition, I do violence to my own opinions. The division of rocks in which that term is adopted is unnecessary and perplexing. I have elsewhere given reasons for not employing it—the following may be mentioned. The Rocks called Transition, are often as purely chemical in composition as any other rock. Many of them contain no organic remains. There is no definite boundary between them as a class and the primary. And lastly it is a division of no practical importance; and one that is very perplexing to the student. In America, they have no line of demarcation, and are often absent altogether. If we place these rocks among the primary, as some Geologists do, we shall then have natural limits to every class-the red sandstone being placed between the primary and secondary-and the chalk between the secondary and tertiary. I shall however retain this name, as I do not consider my own authority sufficient to banish it, |