360 Origin of Carbonaceous Shales. 



down in almost all cases where these plants are found. If the 

 carbonaceous matter of these shales is due to sea-weeds, it is not 

 surprising that it is so generally decomposed. 



Fourth, in addition to the larger forms of sea-weeds, there are 

 many which are microscopic and uni-cellular ; even out in the 

 open ocean they occur in such numbers as to color the water for 

 hundreds of square miles. Some of these, called Zoozanthellm 

 by Brandt, are so associated with the radiolarians as to form 

 self-supporting communities; that is, the algas draw their sup- 

 port from the sea-water,the animals subsisting on the algae. 

 Such organisms exist in overwhelming numbers in both fi'esh 

 and salt water, and must be leaving an important residuum in 

 diffused carbonaceous particles below their places of abode ; we 

 may well believe, therefore, that they have contributed to the 

 formation of such bituminous strata as we are considering. 

 That some part of this carbon may have been derived from 

 the fatty portions of animals, is certainly possible; but their 

 nitrogenized tissues decay with such rapidity, and the^e con- 

 stitute so large a portion of most animal structures, that we 

 must attribute the gi'eater part of this organic matter to the 

 preservation of the more abundant, more carbonaceous and 

 more enduring tissues of plants. 



In nearly all fresh water, and many marine basins, the micros- 

 copic protophytes, diatoms and desmids, swarm in countless num- 

 bers ; the abundance of the diatoms being attested by the exten- 

 sive beds of Tripoli (diatomaceous earth), many feet in thickness 

 and many miles in extent, which are formed of the silicious 

 frustules that have resisted decay. But the desmids and the 

 carbonaceous portions of the diatoms have disappeared as such, 

 yet we have reason to believe that they contributed their car- 

 bonaceous particles to the sediments which accumulated in the 

 basins they inhabited. 



In studying the area occupied by the bituminous shales which 

 have been enumerated, we find they were deposited in shallow 

 and shallowing seas, — the Utica shale in the retreat of the 

 Lower Silurian sea, the Hamilton shales in the narrowed and 

 shallowed basin where the J3evonian limestones had been laid 

 down. The Cleveland shale lies on the Waverley shales, the 

 off-shore deposits of the Carboniferous sea, where the water was 



