150 THE CANADIAN NATURALIST. [Vol. X. 



the Dundas Valley an anticlinal valley, with the slope in each 

 side less than one degree. 



Character of the Rocks. — In New York the lower part of the 

 Niagara formation is represented by 80 feet of dark Ibssilifer- 

 ous calcareo-argillaceous shales ; at Thorold, Ontario, these are 

 much thinner, and at Hamilton and Dundas they are not repre- 

 sented by more than from six to ten feet of muddy sediments 

 (No. 9 of sections), whose upper portions graduate into more 

 calcareous beds. The iieneral character of the series at the 

 western end of Lake Ontario may be repn^sented by the follow- 

 ing section in descending order : 



(a) Thin beds of dark (often limestone and earthy) dok)- 



mites, with shaly partings. Some layers are fossiliferous. . 132 feet. 



(h) Thin beds of light-colored dolomitic rocks, containing 



an abundance of cherty nodules ; fossiliferous 19 feet. 



(c) Dark blue or gray shaly dolomites; fossiliferous 16 feet. 



(c^) Dolomitic compact shales 10 feet. 



(e) Light drab crystalline compact dolomite, in one bed. 5 feet. 



(/) Dark gray compact dolomite, in moderately thick beds, 



the lowest of which contains Pentamerus. 10 feet. 



At Limehouse, only the lower beds are exposed near their junc- 

 tion with the underlying Clinton rocks. Here the deposits con- 

 sist of liglit colored dolomites, of uniform texture in thick compact 

 beds, holding only casts of fossils. 



The representatives of this formation irj Ohio consist of the 

 Dayton limestone of five feet in thickness, succeeded by 60 feet 

 of shales, over wiiich there are 180 feet of limestones, and in 

 Highland County the series is surmounted by 30 feet of sand- 

 stone. In referrinir to these western beds, we find included the 

 Cedarville limestones, beds which are considered of the same 

 horizon as the Guelph dolomites. 



The color of the limestones becomes liuhter on i:;oing' 

 westward, especially after turning a point at Dundas, w^hich 

 formed a right-angled prominent cape in the sea of the Niagara 

 period. Even within a few miles, near Dundas, one can notice 

 the lighter color of the purer calcareous deposits, and at Lime- 

 house, to the north-west of the old cape, coloring matter and 

 shale are almost wanting. 



Composition and Chemical Analysis of the Limestones. — The 

 Niagara limestones, in Canada, consist almost entirely of the 

 double carbonates of lime and magnesia, with a varying per- 



