22 



The Evolution of the Universe 



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4o 



4b 



500 

 I 



5 

 1000 



Miles 



Fig. 8. Map of western United States showing generalized conditions during 

 Triassic and Early Jurassic times. 1, ocean; 2, geosyncline west of the land 

 barrier (stars indicate volcanic centers); 3, geosyncline east of the land barrier; 

 4, areas receiving lesser amounts of deposits; 5, protruding highland areas. 

 (After King.) 



sink deeper into the crust, thus becoming able to receive more 

 sediments. Eventually the sinking trend is reversed and the entire 

 geosyncline is folded and elevated to form linear mountain ranges. 

 Thus, the Himalaya Mountains are composed chiefly of sedimentary 

 rocks formed in the old extensive geosyncline (called the Tethys 

 Sea) which occurred from at least middle Paleozoic time to the 

 middle of Tertiary time, a span of 250 million years or more. The 

 present Mediterranean Sea is the western remnant of the Tethys 



