666 THE JOURNAL OF GEOLOGY. 



ceed directly to estimate the time required to obtain this amount 

 of lime from the land area tributary to the Cordilleran sea. It 

 may be well to make such an estimate on the basis that the 

 area of denudation tributary to the Cordilleran sea in post- 

 middle Cambrian time had 600,000 square miles from which 

 30,000,000 tons of carbonate of lime and 12,000,000 tons 

 of sulphate of lime were derived per annum, 1 if we assume 

 T. Mellard Reade's rate of erosion — of 50 tons of carb- 

 onate of lime and 20 tons of sulphate of lime per square mile 

 per annum. If all of the 42,000,000 tons (equal to 18.8 mile- 

 feet) per annum were deposited within the limits of the Cordil- 

 leran sea, it would have taken 47,790,000 years for the accum- 

 ulation of the carbonate of lime now estimated to have been 

 deposited in the Cordilleran sea. Such a result is manifestly 

 a maximum based on the consideration of one set of phenomena. 

 In addition, however, to this supply of calcium the geographic 

 conditions appear to have been favorable to the free circulation 

 of oceanic currents through the Cordilleran sea, and the tempera- 

 ture was favorable to extensive evaporation and to the develop- 

 ment of organic life, as shown by the occurrence of corals 

 in the middle and upper portions of the Paleozoic, from the 

 Mackenzie river basin on the north to southern Nevada on the 

 south. These conditions would reduce the time necessary for 

 the deposition of the carbonate line. 



Ocean water of the present time contains in solution 

 151.025000 tons of solid matter per cubic mile, which is divided 

 among various salts. A comparison of the matter in the sea 

 and river water shows that the sea contains 3.85 parts of mag- 

 nesium to one of calcium, and river water contains three parts of 

 calcium to one of magnesium. The silica and alumina of the river 

 water disappears in sea water, while the sodium is accumulated. 

 It is from these considerations and the fact that limestones are 



1 Messrs. Murray and Renard consider that organisms have the power of secreting 

 the carbonate of lime from the sulphate of lime contained in the sea water by chemical 

 reaction. For an account of the chemical action that takes place in the sea water, see 

 report of the Deep-Sea Deposits of the Challenger Expedition. 



