AGE OF REPTILES. 258 



you will find in my Natural History, 326. These mon- 

 strous animals, being 25 or 30 feet in length, roamed, el- 

 ephant-like, over the river plains or through the forests, 

 the Iguanodon browsing upon shrubs and trees, and the 

 Megalosaur and Hylaeosaur devouring crocodiles and 

 tortoises. 



358. Cretaceous System. In Europe and Asia the se- 

 ries of rocks belonging to this system is characterized by 

 the presence of sands and sandstones in the lower part, 

 and chalk in the upper part. In this country there is no 

 chalk in the series, but there are beds of sand, clay, marl, 

 and different kinds of limestone. Sandy strata of various 

 kinds and colors predominate. Some are solid, and oth- 

 ers are more or less loose in their structure some so 

 much so that they can be crumbled by the hand. There 

 is a dark green variety called the Green-sand, the great- 

 est part of which, sometimes even to 90 per cent., is sili- 

 cate of iron and potash. There is also a little phosphate 

 of lime in it. It is prized as a fertilizer in New Jersey 

 and other parts of this country, its virtue in this respect 

 coming from the potash and the phosphate. In England 

 the Green-sand gives its name to the whole of the lower 

 part of the Cretaceous series, because it is so prominent 

 in it. Chalk, which is so prominent a part of the series 

 in England and Europe, is, like limestone and marble, a 

 carbonate of lime, but loosely put together in compari- 

 son with them. The chalk is varied in character by the 

 different kinds of impurities that are apt to be mingled 

 with it, and their different proportions. 



359. Localities. In this country the Cretaceous sys- 

 tem comes to the surface over a vastly larger area than 

 the other two series of Mesozoic rocks, the Triassic and 

 Jurassic. It, in fact, made a very large addition to the 

 Xorth American continent in the west and southwest, 

 chiefly west of the Mississippi, though quite largely in 

 the states bordering on the Gulf of Mexico. In the east 

 it appears here and there from New Jersey down to 



