4 BULLETIN OF THE LABORATORIES 



phere during early geological ages, exerted in connection with water 

 a much more powerful and quickening effect in atmospheric and at- 

 mospheric-aqueous action, which must have greatly hastened the denud- 

 ing action during Silurian, Devonian, and early Carboniferous ages, at 

 the same time changing the chemical arrangement and physical form 

 of the rocks. The lowest orders of plant and animal life also fur- 

 nished contributions, which taken in connection with the large 

 amount of organic material represented in some limestone formations, 

 as for instance the Hudson group at Cincinnati Ohio, and the carbon- 

 aceous elements of many of the black shales constituting the Devo- 

 nian and the relatively thin, but very important coal seams, clearly 

 indicate the manifold operations of organic existence, as well as the- 

 inorganic. In addition to this, we have a counterpart to the forma- 

 tion of coral reefs at the present, duplicated to an unusual extent dur- 

 ing the Niagara and lower Devonian, giving rise for example at Louis- 

 ville, Ky., to a barrier which causes the falls of the Ohio. 



An element involving both physical and organic connection is 

 also paramount, as furnishing an index as to the j)osition occupied by 

 the Atlantic ocean. It seems quite apparent that since areas on both 

 sides of its present basin have similarly equivalent, recurring faunas, 

 often quite restricted as in the Cuboids zone, that it was influenced by 

 physical environments which may have also operated in producing 

 sediments for the adjacent coasts, but of this nothing can be said with 

 certainty. Recent surveys have determined the position of three sub- 

 merged mountain ranges running north and south in its central basin. 

 It is certain that at least portions of the Mediterr:)nean have been 

 eroded to an enormous extent, producing material for the adjacent 

 coasts. Before attempting to trace the origin of some of the sedimen- 

 tary rocks subsequent to the Cambrian it will be necessary to deter- 

 mine the land areas existing in Ohio. That the Cincinnati geanticine 

 existed at the close of the lower Silurian, forming an island in south- 

 western Ohio and the adjacent parts of Indiana and Kentucky, is 

 indicated by the absence of upper Silurian and lower Devonian over 

 that area, these formations being deposited on its margins northward. 

 In Tennessee a hiatus is revealed on account of the Devonian black 

 slate resting directly on Lower Silurian beds, clearly indicating the 

 land ares during the upper Silurian and part of the Devonian. This 

 land area had a great influence in building up the subsequent Palae- 

 ozoic rocks, as we shall see further on. 



