626 



HISTORICAL GEOLOGY 



the proportion of size of teeth to length of body holds true in the 

 two species, the giant Tertiary shark (Carcharodon megalodon) attained 

 a length of 70 to 80 feet and possessed jaws five to six feet across. 

 No actual measurements of these sharks have been made, since 

 their skeletons, being cartilaginous, have not been preserved. 



REFERENCES FOR FISHES 



Dean, B., — Fishes Living and Fossil. 



Osborn, H. F., — Age of Mammals, pp. 136, 160, 216, 339-340. 



Invertebrates 



During the Tertiary, limestone strata several thousands of feet 

 thick were built up by the accumulation of the remains of inverte- 

 brates. This is in marked contrast to the deposits formed of verte- 

 brate remains, which are never of great thickness, and seldom form 

 5^**^. even thin beds of great extent. 



i 



J 



Fig. 556. — lertiary Foraminifera: Num- 

 mulites. An enlargement of a portion of 

 the shell is seen in the upper left-hand 

 corner. 



Limestone, locally of enormous 

 thickness and extent, covering 

 areas in the Pyrenees and the Alps 

 mountains, in Greece, northern 

 Africa, Persia, China, and Japan, 

 ii often made up chiefly of the 

 shells of Foraminifera named 

 Nummulites (Latin, nummus, a 

 coin) (Fig. 556) from the shape 

 and size (p. 577). Perhaps at no 

 time in the entire history of the 

 world did an organism of similar 



size live in greater abundance. Other limestones in Europe and on 



the Gulf Coast of North America were formed in large part of other 



forms of Foraminifera. 



Brachiopods and crinoids were rare throughout the period and 



may be considered as races about to become extinct. Sea urchins 



(Fig. 557) continued to be abundant. 



Coral reefs are rare in the Eocene and had a distribution difFerent 



from that of to-day, well-developed reefs occurring on the north and 



south flanks of the Alps and Pyrenees. In the Miocene and Pliocene 



they had almost their present distribution. 



( rastropods and pelecypods (Figs. 558, 559) were abundant through- 



