494 MESOZOIC ERA— AGE OF REPTILES. 



continents as indicated under the last head — proof that, as a general 

 fact, the great inequalities of the earth's crust, which constitute land- 

 surfaces and sea-bottoms, have remained substantially unchanged in 

 position from the first, while steadily increasing in vertical dimensions. 



General Observations on the Mesozoic. 



The Mesozoic, and especially the Jurassic, is characterized by the cul- 

 mination of two great classes of animals, viz., C^halop^ojiJiioIkishs and 

 Reptiles, and one of plants, the Cycads. This is shown in the diagram 

 on page 283. The culmination of reptiles is, of course, its most distin- 

 guishing characteristic. That it was pre-eminently an age of Eeptiles, 

 may be shown by a comparison of its reptilian fauna with that of the 

 present day. There are note, on the whole face of the earth, only six 

 large reptiles over fifteen feet long — two in India, one in Africa, three 

 in America — and none over twenty-five feet long. In the Wealden and 

 Lower Cretaceous of Great Britain alone there were five or six great 

 Dinosaurs twenty to sixty feet long, ten to twelve Crocodilians and 

 Enaliosaurs ten to fifty feet long, besides Pterodactyls, turtles, etc. 

 (Dana). Again, in the Cretaceous of the United States alone the full- 

 ness of rejotilian life was even greater ; for 150 species of reptiles have 

 been found, most of them of gigantic size. Among these were fifty 

 species of Mosasaurs, some seventy to eighty feet long; many huge 

 Dinosaurs, twenty to fifty feet long ; besides Enaliosaurs, Pterosaurs, 

 and gigantic turtles (Cope). These are preserved ! But the known 

 fossil fauna of any period is but a fragment of the actual fauna of that 

 period. Not only did reptiles greatly predominate, but the age seemed 

 to impress its reptilian character on all other higher animals existing at 

 that time. The birds were reptilian birds, the mammals were reptilian 

 mammals. All animals as yet were oviparous (birds and reptiles) or 

 semi-oviparous (marsupials). 



That the climate was then warm and uniform is sufficiently attested 

 by the character of the fauna and flora. All great reptiles and all Cy- 

 cads and Tree-ferns are found now only in tropical or sub-tropical re- 

 gions. This tropical fauna and flora were substantially similar in all 

 latitudes in which the strata have been found — even as far north as 

 Spitzbergen (JSTordenskiold).* During the latter portion of the Creta- 

 ceous period, as indicated by the abundance of deciduous Dicotyls, the 

 climate of North America had become cooler, being about 8° or 10° 

 warmer than now. 



Disturbance which closed the Mesozoic— The disturbance which in 

 America closed the Cretaceous period and the Mesozoic era was an 

 arching of the earth's crust over the whole Plains and Plateau region, 



Geological Magazine, November, 1875. 



