932 HISTORICAL GEOLOGY. 



those that had before occurred in Reptiles. It was progress downward 

 almost indefinitely, but without loss of the essential characteristics of a 

 Mammal. 



The above examples and explanations may serve to illustrate some of the 

 methods by which the modifications of species are supposed to have taken 

 place without the aid of physical catastrophe. 



The great diversity in the characters of Eocene Mammals, wrought out, 

 it is believed, in such quiet times, teach this plainly — that the first period 

 of the Tertiary was exceedingly long, whatever may be gathered to the 

 contrary from some persistent Cretaceous plants. 



OROGENIC AND EPEIROGENIC MOVEMENTS. 



In the opening of the Tertiary era geological history reaches the time 

 when, as mentioned under Dynamical Geology, besides the making of great 

 mountain ranges, nearly all the mountain chains of the world received 

 additions of many thousands of feet to their heights and hundreds of thou- 

 sands of square miles to their areas ; and also when igneous eruptions took 

 place of extraordinary extent. 



1. Orogenic movements at the close of the Nummulitic epoch of the Eocene. — 

 In Europe, the elevation of the Pyrenees, and of some other heights in 

 eastern Europe, occurred after the marine Nummulitic beds of the Eocene 

 had been deposited. The mean direction of the Pyrenees is about N. 80° W. 

 There are large flexures and steep slopes on the side to\\^ard France, but 

 less upturning and gentler slopes toward Spain. 



2. Orogenic movements at the close of the Miocene. — In North America 

 an upturning took place at this epoch along the coast region of California 

 and Oregon, tilting and, in some cases, flexing the Miocene, Eocene, and 

 Cretaceous formations, 5000 feet or more in thickness, as is proved by Mio- 

 cene fossils in the upturned beds (J. D. Whitney). The earlier Jurassic 

 strata are believed to have been earlier upturned and metamorphosed, being 

 of cotemporaneous origin with the Sierra Nevada. 



At this epoch also the great upturning of the Alps and Juras occurred 

 briefly described on page 367. It gave to the mountains the bold flexures 

 of the Mesozoic formations with the overlying Eocene and Miocene, which 

 are a remarkable feature of many of th« lofty summits. The Apennines, 

 according to Stefani, passed through a crisis of upturning and flexures at 

 the close of the Nummulitic Eocene, like the Pyrenees, and also at the close 

 of the Miocene, with the Alps. 



The Himalayas were, to a large extent, beneath the sea during the 

 Nummulitic epoch, and at least 20,000 feet lower than now (page 368). 

 Either directly after this epoch, or before the close of the Miocene, there 

 was an upturning and flexing of the Nummulitic and underlying Cretaceous 

 beds (down to the top of the Carboniferous) and the commencement of the 

 final elevation of the mountain chain. According to the Geological Survey 



