868 HISTORICAL GEOLOGY. 



2. Changes at the dose of the Loiver Cretaceous. — After the earlier 

 Cretaceous, the emergence of the Mexican plateau took place, shutting off 

 the Atlantic waters from the Pacific ; and at the same time, movement 

 change occurred in Texas. According to Hill, faults and flexures were 

 produced, especially in the vicinity of Austin. The general direction of 

 the faults in the region is N. 20° E. The amount of displacement is gen- 

 erally less than 100 feet ; but in the chief fault it is 500 to 750 feet, and 

 the course is marked by an escarpment 100 to 250 feet high. Along the 

 faults the beds are in some places flexed, and the limestone is rendered 

 crystalline. Moreover, there is aii abrupt transition in species in passing 

 from the Lower to the Upper Cretaceous. The Potomac beds, of the 

 Atlantic border, underwent some change in level and some surface erosion ; 

 but no upturning. 



On the Calif ornia coast the continuity of the Shasta-Chico series indicates 

 that the general subsidence mentioned by Diller as in progress during the 

 Cretaceous period was not interrupted at the close of the Lower Cretaceous, 

 But in Western British America, the increased subsidence which introduced 

 the Upper Cretaceous, and spread the sea over the Continental Interior, is 

 supposed by G. M. Dawson (1890) to be marked in a deposit of marine 

 conglomerates, occurring in many places in the southern part of British 

 Columbia, in the Queen Charlotte Islands, northward about the Upper 

 Yukon, and eastward along the line of the Rocky Mountains. Dawson 

 reports also that at this stage of the Cretaceous, or near it, there was 

 renewed volcanic activity in the Queen Charlotte Islands and in the Kocky 

 Mountain Range. 



BIOLOGICAL CHANGES AND PROGRESS. 



Part of the biological history of Mesozoic time has already been reviewed. 

 Still greater changes took place in this later portion, and these now come 

 under consideration. 



Plants : Cycads, Angiosperms, Palms. — The Cycads, the most charac- 

 teristic feature of the Triassic and Jurassic, had their maximum develop- 

 ment during the latter period. They were still prominent, however, in the 

 forests of the Early Cretaceous, and flourished even in the Arctic regions 

 on G-reenland, Spitzbergen, and Alaska; but they were subordinate to the 

 Conifers, and, in the Upper Cretaceous, to the Angiosperms. At present 

 there are only about 50 species of Cycads. 



The line leading up to Angiosperms is uncertain. It is a notable fact 

 that remains of plants of this class are wholly absent from the Wealden of 

 England and from the Kootanie of America, and that only one species of 

 doubted locality has been reported from the Neocomian of Europe. The 

 75 species identified by Fontaine from the fossil leaves of the Potomac 

 formation of eastern America show that the trees were then well established 

 in the American forests, although Conifers were by far the more numerous. 

 But still, as Fontaine shows, they leave their origin unexplained. 



