"210 C. SCHUCHERT THE NORTH AMERICAN GEOSYNCLINES 



basins, as was done, it is true, for the first time by Dana, is to befog the 

 brilliant idea of James Hall. Our understanding of geosynclines (both 

 monogeos}Ticlines and polygeos}Ticlines) is that they are variably long 

 and variably wide, very mobile, sinking areas that always originate within 

 a continent; they are more or less long in geologic development, and 

 receive great quantities of sediments derived in the main from the border- 

 lands. The more rapidly sinking side of a geosyncline is adjacent to the 

 inner side of a borderland, while the subsidence of the trough becomes 

 less and less toward the neutral area of the continent. Finally, when 

 orogenic forces have converted the geosyncline into synclinorial moun- 

 tains, these either are the inner portion of the anticlinorial borderlands, 

 or they occur on one or both sides of geanticlines. 



Mediterraneans are vastly greater fields of diastrophism, with the long- 

 est and most intricate of geologic histories. Of ancient Tethys, the west- 

 ern end still persists as the Roman Mediterranean, with depths down to 

 14,700 feet. Contrast these ocean-like basins with the shallow- water 

 ;geos}Ticlines, whose average depth is several hundred feet, and it becomes 

 I)lain that the two types of marine waters can not be grouped together 

 nnder one term. 



We have seen that all the geosynclines of IS'orth America have become 

 •dry land and mountainous. Into what are the mediterraneans evolving ? 

 We know that Tethys, formerly extending from Asia Minor to Burma, 

 has been converted during the Cenozoic into dry mountainous land across 

 5,000 miles. Seemingly the whole of the Roman Mediterranean is des- 

 tined to the same end, but eastern Tethys throughout the length of the 

 Dutch East Indies is in the main foundering with its mountains perma- 

 nentl}^ into the oceanic depths. The American mediterranean is to a 

 lesser extent doing the same, since Antillia is breaking down into the 

 Caribbean and the Atlantic. 



It appears that once a region is folded through lateral pressure, it 

 rarely redevelops a geosyncline. This is most easily seen in the Atlantic 

 type of troughs, since neither the Appalachian, Acadian, or Franklinian 

 geos3'ncline has gone through even a partial second cycle of geosynclinal 

 formation. On the other hand, the "Kratogens,'^ once the area of the 

 most ancient geosynclines, may, after they are peneplained, be widely 

 flooded by epeiric seas. This was the case with the Canadian shield, and 

 the roots of the Paleozoic Alps of Europe have been widely transgressed 

 by Mesozoic seas. These floods are, however, not those of geos}Ticlines. 

 Nor do geanticlines or borderlands develop geosynclines. Therefore it 

 may be assumed that a region once folded and made positive, becomes 

 stilf and resistant, and that, as a rule, it will remain so throughout time. 



