392 



THE SOUTHERN PLANTER. 



[July 



(1). Primary Rocks. These are tlie 

 lowest in the series, and rest upon unstrati- 

 fied masses beneath, as at (10). They con- 

 sist chiefly of — (1) Gneiss, which has been 

 heretofore described. (2) Mica-slate^ com- 

 posed mostly of quartz and mica, the latter 

 being in such quantity and form as to give 

 a slaty structure to the mass. (3) Talcose- 

 slate, similar to the last, but having talc in 

 the place of mica. The same rock often 

 contains portions of both mica and feldspar. 

 The suface of this slate has a glistening ap- 

 pearance and generally feels somewhat greasy 

 when rubbed with the fingers, but not to 

 the same degree as pure talc or soapstone. 

 (4) Hornblende-slate, a compound mineral 

 in which hornblende is mingled with quartz, 

 clay and feldspar. (5) Clay-slate, which 

 has been described as a finely granular 

 rock in thin layers. Its structure is fre- 

 quently such in this formation, that it can 

 be split into tiles for covering houses; and 

 when dressed off and framed it forms the 

 "slates" used in schools. (6) Sandstones 

 of various shades of color abound amongst 

 the ' primary rocks. (7) Limestones are 

 very often found interstratified with the 

 slates and sandstones of this formation. The 

 Primary stratified rocks, are also called 

 Metamorphic Rocks," in reference to the 

 cJianges of structure through which they 

 have passed, un*der the influence of heat 

 from the igneous rocks upon which they 

 rest. The term " Hypozoic" is also applied 

 to them, in allusion to their position in the 

 geologic series being helow all the rocks 

 containing the relics of animal life. They 

 contain no fossils. 



We have an example of the class of rocks 

 just described, covering a large part of the 

 slope of country commencing on the eastern 

 side of the Blue Ridge and extending 

 nearly to the head of tide-water. Richmond, 

 Petersburg and Fredericksburg, are each 

 situated near the eastern margin of that 

 section of the State, in which these strata 

 are developed at the surface. 



(2). The Silurian Formation lies next 

 in order above the Primary. It has some 

 subdivisions of which we shall take no 

 notice. The rocks entering most largely 

 into its structure are limestones in great 

 abundance, several varieties of slate, sand- 

 stones and conglomerates. 



Fossil shells, coral and encrinites abound 

 in some parts of this forn)ation ; but we 

 cannot enter into any description of these — 

 nor do they have any direct relation to agri- 



culture, except so far as their presence in . 

 the rocks has had an influence upon the 

 quality of soils. 



The Silurian rocks are largely developed 

 on the west side of the Blue Ridge, occupy- 

 ing the whole Valley from New York to 

 Alabama, and embracing several mountain 

 ridges and smaller valleys lying along the 

 western margin of the great valley. 



(3) . The Old-Red Sandstone, or De- 

 vonian,!^ the next formation in regular order. 

 It rests upon the upper part of the Silurian, 

 and dips westward beneath the coal-bearing 

 strata, which occupy so large a portion of 

 Western Virginia. Sandstones, slates and 

 conglomerates,'^ are the prevailing rocks of 

 this formation. 



(4) . The carhoniferous formation lying 

 above the Devonian, is distinguished chiefly 

 by the immense beds of mineral coal found 

 in it. The coal is found in seams or strata 

 of various degrees of thickness, with inter- 

 vening stata of slates and sandstones. The 

 lower part of this formation, in some places, 

 contains large quantities of limestone ex- 

 tending beneath the coal, and cropping out, 

 sometimes very largely, around the margins 

 of the coal fields. The extensive limestone 

 formation of Greenbrier county, running 

 northward into Pocahontas, and southward, 

 with varying width, entirely across Tennes- 

 see and into Alabama, is of the character 

 just alluded to. On the western side of the 

 same coal-field, this limestone is extensively 

 developed in Tennessee and Kentucky. 



(5) . Passing still further upward through 

 the series of fossilliferous rocks, we come 

 next to the New-Red Sandstone, which, in 

 some countries, forms the boundary of the 

 Coal Formation above, as the Old Red forms 

 its boundary below. It is a singular fact, 

 however, that this class of rocks is not 

 found covering any part of our great West- 

 ern coal-fields. We shall not stop to trace 

 out its subdivisions into Upper and Lower 

 New-Red, Permian, &c. The following 

 notice of the geographical distribution of 

 this formation is from Prof. H. D. Rogers' 

 outline of the " Geology of the U. S. and 

 Br. America," published in Johnston's 

 Physical Atlas : — "The largest belt of all, 

 or that of the Middle and Southern States, 

 stretches from the west bank of the Hudson 

 River, where it is upon the level of the 

 ocean, inland in a S. W. direction along the 



* Conglomerates are rocks formed by rounded 

 pebbles cemented firmly together, making very 

 lirm and strong masses. 



