LAND AND WATER 27 



and finally the Donetz coalfield in Russia, where this arm 

 rejoined the ocean. 



The secondary period opens with the Trias. It was an epoch 

 of comparative calm during which the ocean probably 

 experienced slow oscillations, the continents either increasing 

 or shrinking in size ; but there was no more crumpling on a 

 scale that could raise long mountain chains thousands of metres 

 high ; on the contrary, it was the period in which the 

 Hercynian chain was destroyed. The general configuration of 

 the continents and the seas was but little different from that 

 just described. During the Triassic epoch all the northern 

 continents were united ; only the north-west of Siberia, 

 Alaska, and the western side of the United States and Mexico 

 remaining submerged. A vast ocean, bounded on the south by 

 the Pacific continent, occupied the site of the present North 

 Pacific. The Gondwana continent was greatly extended ; 

 to the north, separating it from the North Atlantic, there was 

 a large channel representing the inland sea or Tethys of the 

 preceding age. Two arms of the sea flowing between the Pacific 

 continent and the west coast of America on the one hand, and 

 the east coast of Asia on the other, united the Tethys to an 

 Arctic ocean, which continued its course southwards between 

 the Pacific continent and the equatorial continent of Gondwana. 

 These long channels alternately widened and narrowed in 

 certain places, which was responsible for the three series of 

 littoral deposits of the French Trias in the future Rhone 

 valley, which gives the name Trias to the general deposits of 

 this epoch. 



This general arrangement lasted throughout the Jurassic 

 period ; the North Atlantic continent persisted throughout, 

 although the sea nibbled at its coasts from time to time during 

 the lower Oolic epoch. It was only from the Oxfordian 

 epoch onwards that a depression in the Ural region separated 

 it from the new Sino-Siberian continent to winch it had been 

 united during the Permian. This last remained above water 

 throughout this period, except for the eroded coasts in the 

 extreme north of Siberia and in Borneo during the Lias, the 

 coast of Okutsk up to the Bajocian and the whole northern 

 part of Siberia up to the Portlandian. The Gondwana continent 

 was likewise cut in two by a depression in the region of 



