350 77/r American Geologist, December, IBM 
known of the volume of water discharged into the ocean per year, the 
average amount of material in chemical solution, and the area of land 
surface drained by the rivers, that an average of 100 tons of rocky 
matter is dissolved per English square mile per annum. Of this he 
says: "If we allot 50 tons to carbonate of lime, 20 tons to sulphate of 
lime, 7 to silica, 4 to carbonate of magnesia, 4 to sulphate of magnesia, 
1 to peroxide of iron, 8 to chloride of sodium, and G to the alkaline 
carbonates and sulphates we shall probably be as near the truth a6 
present data will allow us to come."* By the use of the data given by 
Mr. John Murray, in a paper on the total annual rainfall on the land of 
the globe, and the relation of rainfall to the discharge of rivers,t I 
obtain 113 tons as the total amount of matter in solution discharged 
into the Atlantic basin per annum from each square mile of area 
drained into it. Of this 49 tons consist of carbonate of lime and 5.5 
tons of sulphate and phosphate of lime.* 
Mechanical sediments. With the geographic conditions described 
as prevailing during Paleozoic time, the source of mechanical sedi- 
ments later than the middle Cambrian must have been from the broken 
area on the eastern side that extended 100 or 200 miles to the eastward 
and to a much greater extent from the land along the western side of 
the sea. The enormous deposit of from 10,000 to 20,000 feet of mechan- 
ical sediments in early Cambrian time is explained by the assumption 
of favorable topographic conditions of denudation following the Al- 
gonkian revolution and the presence of a land area over the interior por- 
tion of the continent and also, in all probability, between the western 
side of the Cordilleran sea and the western border of the continent. 
During this period the conformable pre-fossiliferous strata of the 
Cambrian accumulated and about 6,000 feet of the lower fossiliferous 
rocks as they occur in the Eureka district of central Nevada. Follow- 
ing the depression of the continent, which carried down the central 
area and also introduced the upper Cambrian (Mississippian) sea into 
the Rocky mountain area of Colorado, etc., there were deposited of 
mechanical sediments in central Nevada: 
Ordovician sands 500 feet 
Devonian fine argillaceous muds 2,000 " 
Lower Carboniferous sands 3,000 " 
Upper Carboniferous conglomerate and sands 2,000 " 
7,500 " 
making a total of 7,500 feet of mechanical sediments, the remaining por- 
tion of the section (15,150 feet) being limestone. 
The following table exhibits the relative thickness of mechanical and 
chemical deposits in the Cordilleran sea, after the middle Cambrian 
subsidence: 
*Loc. cit., p. 229. 
tScottish (ieol. Mag., vol. :!, 1887, pp. 05-77. 
JTotal amount removed in solution per annum by rivers, 702,587 tons per cable 
mile of river water. Total discharge of river water per annum into the Atlantic, 
3,947 cubic miles. Area drained, 20,400.000 square miles. Amount of carbonate of 
lime per annum. 320,710 tons per cubic mile of river water; of sulphate and phos- 
phate of lime, 37,274 tons. 
