138 



Geology of Soils. 



Vol. IX. 



v;mia ; while its easily accessible situation 

 will enable many of your readers to verify 

 the correctness of my observations. Instead 

 of commencing at one extremity of tliis 

 section, I shall, in order to make the con- 

 trast between the soils overlying different 

 rocks more striking, begin at a well known 

 and easily defined line in it; that is, the 

 limestone valley which passes through the 

 counties of Montgomery and Chester, and 

 generally known as the " Great Valley of 

 Chester county." The rock of this valley 

 is generally a stratified primary limestone, 

 and the soil which covers it, has always 

 been held in high estimation for its fertility 

 since the first settlement of the country. 

 There are to be found in it occasionally 

 ridges of other varieties of rock, the soil 

 over which is generally of an inferior qual- 

 ity. Immediately adjoining this vallev on 

 the south, is a range of talcose-slate hills, 

 the soil on which has been as long noted 

 for its inferiority; this soil is made up in 

 a great measure of very minute particles 

 of the slate, and so unfavourable are they 

 to fertility, that lying more elevated than 

 the limestone, they are carried over it by 

 torrents of water and other means, and just 

 so far as they reach, and in proportion to 

 the quantity transported, do they impair the 

 fertility of the soil covermg the limestone. 

 South of the talcose-slate, there extends for 

 several miles, in the neighbourhood of West 

 Chester, a ledge of a variety of serpentine 

 rock, the soil over which is so notoriously 

 unproductive, and so incorrigibly refractory, 

 as to have obtained the local name of the 

 barrens, and the. rock, that of the barren 

 rock. The same kind of soil covers this 

 rock wherever it is observed near the sur- 

 face in that part of the State. Immediately 

 south of this serpentine ledge, we come to 

 horiiblcndic and gneiss rocks of several va- 

 rieties, many of them in a disintegrating 

 state, tliG soil over which is highly prtxluc- 

 tive, and the change from one to the other 

 is so sudden, that in many places it is not 

 100 yards from deplorably sterile, to highly 

 fertile land. A"nd this too, under a very 

 similar general management, the whole 

 being occupied by as industrious, intelligent 

 and enterprising a set of farmers as can be 

 found in any other part of the Union. Con- 

 tinuing our examinations southwardly, the 

 same class of priiniry rocks, in all the Pro- 

 tean shapes fur which they are so remark- 

 able, appear to form the underlying rock of 

 the country until they disappear under the 

 tertiary and diluvial series of the tide-water 

 region. Changes of soil, accompanying 

 every important change in the underlyiu'i- 

 rock over this district, can be readily per- 



ceived by an attentive observe!-, although 

 owing to the numerous windings, changes 

 and alternations of the different varieties of 

 these rocks with each other, these changes 

 of soil cannot be pointed out on paper with- 

 out a minute and vokiminous description of 

 the country. But over them all, except the 

 limestone, the soil will be found to be made 

 up in great measure of very minute frag- 

 ments of the rock immediately underlying 

 it, or of those in its vicinity; or of such 

 substances as it is known these rocks are 

 converted into by decomposition. 



Commencing our examinations again at 

 the limestone valley of Chester county, 

 and pursuing a northwardly course, we 

 first come to a hill of sandstone, consi- 

 dered by Professor Rogers as the lowest 

 in our secondary series, and denominated 

 by him No. 1. The soil on this is of a light- 

 ish colour, and is considered of an inferior 

 quality for agricultural purposes. It is most- 

 ly kept in wood for the supply of the neigh- 

 bouring farms. Next comes, in the county 

 of Chester, a strip of primary rocks, a prin- 

 cipal ingredient of which is feldspar. The 

 remains of this rock, particularly the quartz 

 parts of it, are found plentifiiUy distributed 

 through the soil, which is generally held in 

 good estimation by farmers. We next pass 

 over a formation of red shale, sandstones and 

 conglomerates, extending to the primary 

 rocks of the South Mountain, near Reading. 

 The soil over these shales and sandstones, 

 partake of the colour and materials of the 

 imderlying rock; in some places it is very 

 fertile, in others it rises into poor, rugged 

 and stoney hills. Opposite to these, on the 

 eastern side of Schuylkill, we find an ex- 

 tensive deposit of red, or rather reddish 

 brown, shaley sandstones, belonging to the 

 upper secondary series, they overlay and hide 

 from view the strip of primary rocks above 

 mentioned. They are also protruded through 

 in many places liy hills of greenstone-trap. 

 The soil over these shales partakes of the 

 colour and materials of the rocks below, and 

 is moderately fertile, while the soil covering 

 the greenstone-trap, and immediately around 

 it, and apparently derived from it, is so poor 

 as not to repay the labour of cultivation, 

 without first incurring a heavy expense in 

 manuring and reclaiming it. Over these 

 shales, and apparently forming the highest 

 member of the series, a deposit of calcare- 

 ous brescia is found ; this is the same form- 

 ation, which further westward, is called Po- 

 tomac marble, and from which the pillars in 

 the Capitol at Washington, were procured. 

 This rock, from its heterogeneous composi- 

 tion, is familiarly termed all sorts. Adjoin- 

 ing tliis, but lying unconformably with it, is 



