SUMMATION AND CONCLUSIONS 209^ 



next ask the even more significant question, Why is it that western North 

 America, in direct contact with the greatest ocean, exhibits but little 

 orogeny until Jurassic time ? We have seen that in eastern North Amer- 

 ica, mountain-making was very active in late Devonian and again in 

 Permian times; in Europe at the close of the Silurian and several times- 

 during the Carboniferous. Do these facts, then, mean that the North' 

 Atlantic (^Poseidon) was an actively sinking ocean during the Paleo- 

 zoic, while the North Pacific was not a markedly subsiding area until 

 early Mesozoic time? 



In further elaboration of these surmises, we note the greater volume of 

 the sediments of the Appalachian, Acadian, and Franklinian geosynclines, 

 when contrasted for each period with those of the Cordilleran trough,, 

 which shows that the borderland Cascadia was less often reelevated than 

 were the eastern borderlands Appalachia and Acadia. On the other hand,, 

 in western North America, from Alberta south to Nevada, the greater 

 part of the Ordovician and most of the Silurian are poorly represented 

 by sediments, again showing that the Atlantic was cliastrophically active' 

 earlier than the Pacific. We may therefore speak of Atlantic and Pacific 

 types of geosynclines, since the same relations of parts are also true for 

 South America. 



We must also ask ourselves, Why are there periodically rising border- 

 lands with geosynclines along their inner sides? They appear to be the 

 compensating areas of subcrustal flowage between the subsiding oceans 

 and the unmoved or horst-like neutral areas or "Kratogens" of the posi- 

 tive continents. 



We will now consider the mesogeosynclines. It has been shown that 

 all of the geosynclines of North America form on the inner sides of bor- 

 derlands which are but the diastrophically active margins of the conti- 

 nent. Furthermore, that geosynclines are destined to evolve into moun- 

 tains. This is the American theory of geosynclines, and it is in direct 

 opposition to the views of European geologists, especially as formulated 

 by Haug in 1900. The fundamental difference between the two theories- 

 is that Haug places the geosynclines on the outer sides of the continents 

 in the areas of the continental shelves (figure 18). His studies center in 

 the history of Tethys, the greater Mediterranean, once extending from 

 the Atlantic to the Pacific. This is a very deep and vast basin of the 

 oceanic type, situated, however, between close-lying continents. Tethys 

 was not, therefore, a geosyncline in the American sense, but a mediter- 

 ranean or mesogeosyncline. 



To extend the meaning of the term geosyncline to all subsiding areas 

 of sedimentary accumulation, to mediterranean and even to oceanic- 



