390 E. C. ANDREWS THE HYPOTHESIS OF MOUNTAIN FORMATION 



several periods, such as the Eocene, Miocene, Pliocene, and in places the 

 earlier part of the Pleistocene. 



The land crests or plateaus formed during the earlier uplifts were re- 

 duced, possibly, to the stao;e of ^'rolling downs'' or wide plains prior to 

 the revival of uplift at later stages in the Cenozoic. 



The present forms appear to be pressure ridges with flattish or undu- 

 lating tops and with edges warped or faulted down to intermontane val- 

 leys of structural origin. Powell's Uinta and the Eockj^ Mountain front 

 are types. The Atlantic mountains indicate a feebler response, in the 

 form of a complete earth wave, to the same dominant control. 



The western side of the Sierra, together with the land trough of the 

 Californian Valley, affords a magnificent example of warping during the 

 later portion of the Cenozoic. The foldings of the Pliocene and of the 

 Pleistocene on the Californian coast are examples also of a type of struc- 

 ture girdling the real Pacific on the east. 



EUROPEAN MOUNTAINS 



These appear to be replicas, on a smaller scale, of the Asiatic forms 

 which began with the upheaval of the Tethyan bed. 



AFRICAN MOUNTAINS 



These may be described as similar to those of the other continents, but 

 their formation has not been under the direct control either of the Pacific 

 or Tethyan regions. 



AUSTRALIAN MOUNTAINS 



These are plateaus relatively low in height and formed within dense 

 rocks. The younger and less compacted rock ty]3es occur within the great 

 plains of the center. The surfaces of the plateaus are undulating, the 

 margins being warped and faulted. This fact is appreciated only in the 

 regions of unfolded rock types, such as those of the Permo-Carboniferous 

 at the Bacchus Marsh scarp in Victoria, the Trias- Jura of the Blue 

 Mountains in New South Wales, the Trias-Jura conglomerate flanking 

 the slopes of New England, and the Darling Downs, in New South Wales 

 and Queensland respectively. In the closely folded Paleozoic rocks which 

 form the general surface of the great plateaus of eastern Australia, the 

 warping, with faulting of the margins, is not discernible with ease. 

 Nevertheless, it is implied by the continuity of the general form of the 

 plateau margins themselves, which are traceable through the area of hori- 

 zontal rocks to the areas of slate where the rocks have been closelv folded. 



