650 



THE JOURNAL OF GEOLOGY. 



mechanical and chemical deposits in the Cordilleran sea after 

 the middle Cambrian subsidence : 



Mechanical Sediment, 

 Chemical Sediment, 

 Ratio, - 



Wasatch. 



10,000 

 10,400 



Central 



Nevada. 



7,500 

 15,150 



I" 



Southwest 

 Nevada. 



2,500 

 13,000 



Montana. 



1,000 



4,000 



Alberta. 



4,600 

 15,000 



If an average is taken of the mechanical sediment deposited 

 subsequent to the close of middle Cambrian time, it will be found 

 to be about 5,000 feet for the entire area, which, I think, does 

 away with any necessity to assume an additional hypothetical 

 land area for the source of the mechanical sediment. The fine 

 sand composing the quartzites and the silt forming the shales, as 

 well as the fine conglomerate of later deposits, were derived from 

 the adjoining land areas, and, in all probability, currents swept 

 through from the ocean to the south or north, distributing the 

 mud and sand contributed from the rivers and streams along the 

 shores. 



Chemical Sediments. — The present supply of the carbonate of 

 lime, silica, etc., contained in sea-water is derived from waters 

 poured into the sea by rivers and streams. The Cordilleran sea 

 undoubtedly received a large contribution from the adjoining 

 land areas, but a considerable amount was possibly derived from 

 an oceanic current that circulated through it as the southern 

 equatorial current of the Atlantic now sweeps through the 

 Caribbean. From the vast deposits of carbonate of lime it 

 might be assumed, a priori, that the waters of a Mississippi or 

 Amazon were poured into it, but there is not any evidence of 

 the existence of such a river, although the tributary area may 

 have been very large in Cambrian and Carboniferous time, if the 

 drainage of the country west of Hudson's Bay was to the west- 

 ward. 



Conditions of Depositio?i. — With free communication into the 

 open ocean on the south, and probably on the north, during 

 most of Paleozoic time strong currents must have circulated 

 through the Cordilleran sea. The broad distribution of 



