194 Scientific Geology. 



tained in this osseous conglomerate: and that in two instances, I 

 found the bones penetrated by a cylindrical cavity, two or three inches 

 long ; pretty obviously the work of some lithodomous shell. 



We ascertain, then, with considerable confidence, the remains of 

 the crocodile and two or three species of sharks in this cliff. Very 

 probably an experienced comparative anatomist may detect other spe- 

 cies among the bones which I have obtained. 



The largest shark's tooth given on the plate, (Fig. 12,) is consid- 

 erably broken ; and, therefore, its exact dimensions cannot be ascer- 

 tained : but the following measurement certainly does not exceed the 

 truth. 



Greatest breadth of the part covered with enamel, meas- 

 ured across the base, ...... 2 inches. 



The length measured on the enamel of the concave part 

 of the tooth, 2 inches. 



If we estimate the size of the shark to which this tooth belonged, 

 according to the principles adopted by the Count Lacepede and Fau- 

 jas St. Fond, in the " Annales de Museum," its length must have been 

 about 50 feet ! Dr. Knox, however, thinks this estimate too high.* 

 But he describes a shark killed on the coast of Africa, as having teeth 

 which measured 11-2 inch in the directions mentioned above. Sup- 

 posing the relative size of the teeth to indicate the relative size of the 

 animals, the fossil shark at Gay Head must have been about 36 feet 

 long ! And some of the vertebrae there, that have been described, 

 correspond with a bulk so enormous. Such was one of the animals 

 that swam in the ancient seas of this latitude ! And this result cor- 

 responds with the conclusions of European geologists, that the ex- 

 tinct animals were generally much larger than those now existing. 

 The tooth of the crocodile at Gay Head, as well as the great size of 

 some of the sharks bones, show, also, that when these animals swam 

 in the waters of our continent, the climate must have approximated 

 to a tropical character : a conclusion, which, in respect to Europe, 

 has been well established by a multitude of similar facts. 



I have already remarked that I had not met with any account of 

 an osseous conglomerate like that at Gay Head, in any of the Euro- 

 pean formations of plastic clay. But bones of vertebral animals do 

 occur in one place, at least, in the clay beds of the Paris basin. " M. 

 Bequerel," say Cuvier and Brogniart, " has found in the same bank 



* Edinburgh Journal of Science, Vol. 5. p. 16. 



