WESTERN DISTRICT. 277 



which compose the rocks whose analyses we have just given. From the Niagara lime- 

 stone, upon which tlie red shale and marl repose, up to the Oriskany sandstone, the mate- 

 rials are all extremclj' fine, excepting a thin sandy Ijand near the (oji of tiie red slate. 

 For seven or eight hundred feet, then, the rocks which form a large body of soil are in 

 tliat condition as it regards size, ■which fits them for the most effectual action of the roots 

 of plants, and for the solution so necessary to prepare them to be received into the texture 

 of the plant. The fineness is not such as to pass readily into an impalpable state ; such, 

 for instance, as is at all liable to pack, and thereby exclude air and moisture. We regard 

 the condition we have here described as quite desirable for wheat, and all other crops 

 which admit of higii cultivation. 



The origin of the materials constituting these shaly rocks can not be determined with 

 certainty. That they were not the immediate result of abrasion from primary rocks is 

 certain, inasmuch as their fineness could not have been effected by such an operation, 

 unless indeed the materials should be regarded as having been transported far from their 

 parent rock ; and, besides, we are unable to detect, by a common microscope, any grains 

 of felspar or mica, or the products of any primary rocks, except fine rounded grains of 

 quartz. A fact which bears upon the question under consideration, is, that no fossils are 

 known in the red and 'green shales, those deposits which are so exceedingly fine ; and 

 this fact seems to favor the view that the deposition actually took place in a deep sea, at a 

 depth at which organic beings are not known to exist. 



The rock, which succeeds the Onondaga limestone, is the Marcellus slate ; and it is so 

 closely related to the shales below, that its composition may be given in this place. The 

 rock is of course thin-bedded and liable to disintegration, and is therefore usuallj' con- • 

 cealed at its outcrop. It is calcareous in many places, and at some points it appears that 

 an unusual quantity of lime was deposited with the slate, as a large quantity of septaria 

 is inclosed between the layers at such places ; at other places, thin bands of limestone 

 appear. 



The shales, in their most common condition, are composed of the following substances : 



■ Water of absorption 2-00 



Organic matter 2"25 



Silex 48-12 



Peroxide of iron and alumina 10*00 



Carbonate of lime 36 -GO 



Magnesia 1-00 



100-07 



The vegetable or organic matter is quite as abundant as in the green shales, but it is more 

 carbonaceous, or charred, and hence the dark color imder which the rock usually appears. 

 Sometimes, however, the dark color is due to the presence of decomposing pyrites. 



The passage from the Marcellus shales to the Hamilton group is easy, and is effected 

 by an increase of siliceous matter in a coarser state ; besides this change, we may often 



