602 



GEOLOftT OF OHIO. 



bslieved that the clay is the result of the decomposition of the overlying 

 Corniferous limestone, and not a product of original deposition. Such 

 accumulations are very common along the outcrops of limestone forma- 

 tions, and notably, in the seams and crevices of the State quarries, but 

 whenever they have this origin, they betray it by the silicious frag- 

 ments of rock or fossils that they enclose. The clay here referred to is 

 very fine-grained and homogeneous, is either white or red in color and 

 contains no recognizable foreign fragments. It may, therefore, be taken 

 to mark a change in the character of the seas in which the underlying 

 limestone had so long been forming, and it may be added that other in- 

 dications, derived from their chemical analysis, point in the same direc- 

 tion. 



Their composition is shown in the following analyses, made for the 

 Survey by Professor Wormley, number 1, being the red variety and 

 number 2, the white variety just named. Both saodples were taken 

 from the bank of Big Darby on the John Phillips farm, one mile below 

 Georgesville : 



The dissimilarity in composition is so great as to forbid their reference 

 to a common origin and especially to the weathering of the adjacent 

 limestone. 



It has already been remarked that this limestone is magnesian in 

 character. The composition of some of its phases is shown in the fol- 

 lowing analyses. It may be added that the concretionary masses give 

 promise of making a hydraulic cement. At least they do not readily 

 burn into lime : 



