Crosby.] 472 [November 7, 



teeth forming the nuclei of the nodules and which are frequently 

 brought up uncoated with foreign matter, 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 indistinguish- 

 able from the huge teeth found in the Eocene beds." On this 

 point Mr. John Murray, also of the "Challenger" scientific staff, 

 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 shark's teeth and between thirty and 

 forty ear-bones of cetaceans ; and we may conclude with great 

 certainty that the clays of these oceanic basins have accumulated 

 with great slowness." He also says: "It is indeed almost beyond 

 question that the red clay regions of the Central Pacific contain 

 accumulations belonging to geological "ages different from our 

 own." Again, " the shark's teeth, ear-bones, manganese-nodules, 

 altered volcanic fragments, zeolites, and cosmic dust are met with 

 in greatest abundance in the red clays of the Central Pacific, at 

 that point on the earth's surface farthest removed from conti- 

 nental land. They are less abundant in the Radiolarian ooze, are 

 rare in the Globigerina, Diatom, and Pteropod oozes, and they 

 have been dredged in only a few instances in the terrigenous de- 

 posits close to the shore. These substances are present in all the 

 deposits, but owing to the abundance of other matters in the more 

 rapidly forming deposits their presence is masked, and the chance 

 of dredging them is reduced. We may then regard the greater 

 or less abundance of these materials, which are so characteristic 

 of a true red clay, as being a measure of the relative rate of accu- 

 mulation of the marine sediments in which they lie. The terri- 

 genous deposits accumulate most rapidly, then follow in order 

 Pteropod ooze, Globigerina ooze, Diatom ooze, Radiolarian ooze, 

 and, slowest of all, red clay." 



The time since the Eocene, when the large Carcharodons lived, 

 is estimated 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 sediment being probably less 

 than one foot, and possibly not more than two or three inches, in 

 a million years. 



