CRETACEOUS PERIOD. 467 



Climate. — The existence of Belemnites paxillosus and Ammonites biplex 

 (or closely-allied species) in the Arctic, the Andes of South America, 

 and Europe, indicates a remarkable uniformity of climate over the 

 globe in the Jurassic period. No facts connected with the geogra- 

 phical distribution of species are yet ascertained that sustain the 

 idea of a diversity of zones approaching the present. The facts 

 favor the view that the climate of the Arctic in the Jurassic period 

 was at least warm-temperate. 



CRETACEOUS PERIOD (18). 



The Cretaceous period is the closing era of the Reptilian Age. 

 It is remarkable for the number of genera of Mollusks and Rep- 

 tiles which end with it, and also for the appearance, during its 

 progress, of the modern types of plants and fishes. 



The name Cretaceous is from the Latin creta, chalk. The Chalk 

 of England and Europe is one of the rocks of the period. 



1. AMERICAN. 



Epochs. — 1. Epoch of the Earlier Cretaceous- 2. Epoch of the 

 Later Cretaceous. 



It is probable that only the later half of the Cretaceous period of 

 Europe is represented by these epochs in America. 



I. Rocks: kinds and distribution. 



The Cretaceous beds occur (1) at intervals along the Atlantic 

 border south of New York, from New Jersey to South Carolina, (2) 

 extensively over the States along the Gulf border, and (3) through a 

 large part of the Western Interior region, over the slopes of the Rocky 

 Mountains, from Texas northward, to the head-waters of the Mis- 

 souri on the east of the summit of the chain, and far into the 

 Colorado region on the west. Still farther northwest in British 

 America, they appear on the Saskatchewan and Assiniboine,and 

 also on the Arctic Sea, near the mouth of the Mackenzie. North 

 of New York on the Atlantic border they are unknown. 



On the map, p. 133, the Cretaceous areas are indicated by broken 

 lines running obliquely from the right above to the left below: 

 one area crosses New Jersey (the other outcrops on the Atlantic 

 border are too small to be indicated) ; a far more extensive area 

 covers the Gulf States, and another, the region west of the Mis- 

 sissippi. The region along the Gulf border as well as Atlantic, 



