I860.] 



THE SOUTHERN PLANTER. 



395 



some most important elements of mineral 

 fertility. 



The Great Valley of Virginia is an ex- 

 ample of the Silurian formation. The 

 western slope of the Blue Ridge belongs to 

 this. The rocks here, and on the spurs, 

 •which often extend out some (iistance into 

 the valley, are chiefly slate and hard sand- 

 stone. These form light, unproductive soils; 

 and where the rocks are hard sandstones, 

 they disintegrate very slowly, break off in 

 large fragments under the influence of 

 frost, and form rough, unmanageable soils. 

 As we descend into the open valley, we find 

 the formation consisting of a great variety 

 of limestones, with vast beds of interstrati- 

 fied slates and shales,* all containing fossil 

 shells and coral. By their disintegration, 

 these rocks generally give soils of fine 

 quality. In most parts of this valley, the rocks 

 have been very much tilted and warped at 

 the time of their upheaval, thus giving rise 

 to a peculiar and interesting variety of 

 landscape. In many places we meet with 

 abrupt precipices, such as are common 

 along the banks of water-courses ; in other 

 places we find deep gorges, like that spanned 

 by the Natural Bridge ; while the less sub-^ 

 lime but no less beautiful hills, with their! 

 gently undulating slopes and rounded tops, | 

 are found to cover the greater part of the 

 surface throughout the whole 

 breadth of this delightful section 

 State. I 



As century after century has passed | 

 away, the solid rocks, as well as the more: 

 brittle shales, have been gradually broken I 

 down into minute fragments by rain and' 

 frost, while the carbonic acid brought down^ 

 by the rain-water has dissolved out much of; 

 the carbonate of lime, and left the clay to| 

 form soils varying in depth from less than 

 an inch to many feet. The depth of these 

 clay deposits depends partly upon the steep- 

 ness of the land, but still more upon the 

 structure ar.d composition of the rock. If 

 the surface is steep, the greater part of the 

 liberated clay may have been washed down 



length and 

 our 



of 



into some neighbouring valley, formin! 



there a deep, rich soil, and leaving thei 

 rocky hill-side almost naked. If the rocks; 

 were pure carbonate of lime, there could be 

 no residuum of clay and sand to produce 

 soil ; but the truth of the case is, that 



* Shale is a brittle, iinperfect form of slate. 



nearly all the compact limestones contain a 

 considerable amount of these impurities, 

 while some contain not more than fifty per 

 cent, of carbonate of lime; and riiany of 

 the beds of calcareous shale have but a 

 small quantity of the carbonate, combined 

 with a large quantity of clay. These last 

 not only disintegrate more rapidly, but also 

 leave a much larger amount of residuary 

 matter than any of the more solid rocks. 

 Hence we generally find them underlying 

 deep beds of clay. 



The soils resulting from limestone forma- 

 tions are generally productive, and remark- 

 ably well adapted to the culture of grass 

 and grain crops, and also produce good to- 

 bacco. Where the ancient coral reefs are 

 found among the limestones of this forma- 

 tion, the clay which they leave after their 

 decay jj, as well as that formed from the ad- 

 jacent shales, is rich in organic matter, as 

 well as the mineral elements required in 

 soils of the best quality. The author has 

 detected ammonia in very perceptible quali- 

 ties, in clay found in a quarry of coraiine 

 limestone, at a considerable distance be- 

 neath the surface of the ground. If we 

 suppose this ammonia to have been produced 

 in the rock by the decay of the coral, by 

 which it was built up, and then retained by 

 the clay after the rock has been disintegra- 

 ted, and has had its carbonate of lime dis- 

 solved out, it aff"ords us a striking illustra- 

 tion of the tenacity with which ammonia is 

 held by clay. 



The mountain ridges lying along the 

 western side of the valley, belong also to 

 what we have called the Silurian for- 

 mation. Here slate and sandstone prevail. 

 The slate forms a soil capable of considera- 

 ble improvement; but the sandstone is too 

 hard to form a soil suitable for tillage, ex- 

 cept along the lower slopes of the ridges 

 and in the valleys, where the abraded ma- 

 terial has been collecting for many centuries. 



When clay from one ridge is carried 

 down by water, and mingled with the sand 

 brought down from some neighbouring 

 ridge, and deposited along the banks of 

 streams, plants, insects, fresh-water shells, 

 etc., being mingled with it, very fertile bot- 

 tom lands are often formed, running in long 

 narrow strips through extensive sections of 

 almost barren mountains. — (^Eodgers.') 



The soils of the Old Red Sandstone are 

 extremely variable in our country. Where 

 marl and limestone are found in this forma- 



