Crosby.] 504 [March 7, 



erosion, is alone sufficient to prove that the main mass of the range 

 must have been profoundly submerged. We may well suppose, 

 therefore, that the Rocky Mountains formed a submarine ridge in 

 the Paleozoic sea similar to that which now, along a general north- 

 south line, divides the basin of the Atlantic, the higher points only 

 of both the Paleozoic and the Atlantic submarine ridges projecting 

 above the water in widely separated oceanic islands. That the 

 Rocky mountains did not exist as considerable land areas in the 

 Paleozoic sea is shown clearly enough, also, by the general absence, 

 above the Potsdam, of the mechanical sediments which would nec- 

 essarily have been formed by their degradation. 



Perhaps the most important fact having a distinct geological 

 bearing, which we owe to the dredgings carried on in the deeper 

 jDortions of the sea, is the extremely slow rate of deposition over 

 the abyssal areas of the ocean floor. The distance from land and 

 the chemical conditions, almost entirely exclude ordinary mechan- 

 ical and calcareous sediments ; and we find, after crossing the cal- 

 careous and siliceous oozes, only the impalpable red clay, which is 

 the truly abyssal deposit. The following characteristics of the red 

 clay afford ample evidence, as Sir Wyville Thompson and Mr. John 

 Murray have shown, that it accumulates with almost infinite slow- 

 ness : — 



Over the red clay areas, the dredge brings up large numbers of 

 nodules of the iron and manganese per-oxides. "The nodules are 

 evidently formed in the clay, and the formation of the larger ones 

 and the segregation of the material must have required a very long 

 time ; while many of the sharks' teeth forming the nuclei of the 

 nodules belong to species which we have every reason to believe 

 have been extinct since early Tertiary times. Some teeth of a 

 species of Carcharodon are of enormous size, four inches across the 

 base, and are indistinguishable from the huge teeth found in the 

 Eocene beds." On this point Mr. Murray says : "When there has 

 been no reason to suppose that the trawl has sunk more than one 

 or two inches in the clay, we have had in the bag over a hundred 

 sharks' teeth, and between thirty and forty ear-bones of whales." 



The time since the Eocene, when the Carcharodons lived, is es- 

 timated by geologists at more than a million years, and yet enough 

 clay has not been deposited during this immense period to bury the 

 teeth of this giant shark beyond the reach of the dredge ! the rate 

 of increase of the sediments being probably less than one foot, and 



