SECRETARY'S REPORT. 113 



very great depth, with the debris of the rocky materials trans- 

 ported from a distant region, and the material which constitutes 

 the soil is such, as, for the most part, does not exist in its 

 original form in the rocky structure which lies beneath. There- 

 fore the study of the rocks of a large part of such a territory is 

 a matter of comparatively little importance ; but the study of 

 the composition of this drift material, — this gravel, sand and 

 clay, — which constitutes the really available portion of the 

 surface in many districts of the north, is of course essential to 

 the purposes of agriculture, as it is essential to the generaliza- 

 tions of the scientific geologist. But when we proceed to certain 

 sections of the south, we pass beyond the limits of this great 

 northern drift, which, either through the action of glaciers, or 

 of vast moving masses of water, has been swept over so great a 

 portion of the northern hemisphere. When we pass south a 

 certain distance — for example, a little south of the northern 

 limit of Pennsylvania, — we find that this drift covering has 

 become very thin, and soon we find that it has entirely disap- 

 peared. From this, onward, the soil in general, through a vast 

 district of country, has been formed by the disintegration of the 

 subjacent rocks and has its mineral characters determined by 

 the nature of these rocks. Of course, in this remark I do not 

 include the alluvial soil of the valleys, some of which has been 

 transported from northern regions, — for instance, along the 

 northern course of the Susquehannah, — but the main soil of 

 the uplands, and much of that which has been deposited as 

 alluvion is derived from the rocky materials that occupy the 

 /Very surface of the contiguous land. 



Let us now consider some of those great belts of soil thus 

 deriving their materials and qualities from the contiguous geo- 

 logical formations. Commencing our observations, we will 

 suppose; with Long Island and New Jersey, we extend our view 

 along that broad Atlantic plain, having the ocean on its eastern 

 margin, washing it continually with its wearing ripples, and 

 reaching towards the west and north-west as far as the falls of 

 the rivers, where stand Trenton, Philadelphia, Baltimore, Wash- 

 ington, Richmond and Petersburg, curiously enough, all located 

 just at the margin where this great Atlantic plain ceases, and 

 where the broad belt of granite and other so-called primary 

 rocks begins to make its appearance. Now, throughout all 



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