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THE AMEBIC AN NATURALIST [Vol. XLII 



fauna of the Genesee may have been the presence of a 

 sargasso sea as suggested years ago by Newberry for a 

 similar fauna in the Ohio black shales. 30 The Genesee 

 and Ohio black shales, occurring from New York to Vir- 

 ginia and west to Kentucky and Indiana, contain through- 

 out their whole extent some or all of the following small 

 species: Lingula spatulata, L. ligea, Schizobolus concen- 

 tricus, Chonetes scitnlus, Leiorltynclius quadricostatus. 

 These species are not only small, but also thin, the largest 

 or last named being very frequently if not usually crushed 

 through the pressure of the overlying- sediment. This 

 smallness and thinness apparently indicates a habitat for 

 the living animals where they were not subjected to the 

 shock of waves as are shore-living species. 



d. At Windsor, Nova Scotia, a very fossiliferous lime- 

 stone, of Carboniferous age, occurs between conglom- 

 erate, sandstone and a black shale of the same age below 

 and coal measures of sandstone and coal above. The 

 coal is seen in the Joggins region across the bay. The 

 shallow water or terrestrial origin of the former set of 

 beds is indicated by the predominance of the coarse 

 clastic sediment, the presence of ripple marks, footprints 

 and Lepidodendra. A similar origin accounts for the 

 latter. 



The fossils of these Carboniferous limestones show the 

 effect of the unfavorable environment in which they lived 

 at the time these limstones were being deposited. 

 Brachiopods suffer most, being depauperate throughout 

 the series, the pelecypods, though much dwarfed, suffer 

 less diminution, while the cephalopods were the most 

 resistant to the dwarfing agencies; i. e., the more closely 

 a species was confined to a particular habitat the more 

 dwarfed were the resultant adult forms. 



The uniformly small size of most of the species is 

 attributed by Dawson to two causes : 31 



1. Variation in depth and content of the water as 



