202 C. SCHUCHERT THE NORTH AMERICAN GEOSYNCLINES 



17,000 feet. The foundered areas are parts or the whole of mesogeosyn- 

 clines and synclinoria and of geanticlines and anticlinoria. Abendanon 

 has renamed Sino-Australia Aeguinoctia. 



The history of this foundering is still largely nnkno^yn. It probably 

 began in the later Paleozoic, was most active in the later Mesozoic when 

 Australia was separated from Asia, and these negative and positive move- 

 ments have continued through Cenozoic time into the present. In most 

 places along the margins of the continents facing the Pacific we note 

 these great founderings, and the largest of all in the South Pacific. The 

 chief area of crnstal subsidence is, of course, in the water hemisphere, 

 and it may well be that the united pull of the subsiding Antarctic and 

 South Pacific oceans was the cause for the breaking up of Sino-Australia. 

 The inbreaking of the Indian Ocean at the expense of Lemuria and 

 greater Australia was probably also in sympathetic connection with this 

 negative movement of the Antarctic Ocean. 



In the Atlantic Ocean there is nothing comparable to this foundering 

 of the Pacific. The relations are rather with the type of foundering in 

 the Indian Ocean. Western Gondwanaland, uniting Africa to Brazil, 

 was not in existence after Lower Cretaceous times, though there is much 

 marine faunal evidence back of the latest Jurassic down to the Silurian, 

 proving the existence of a land across the equatorial Atlantic. The foun- 

 dering in the Atlantic began about the same time as that in the Indian, 

 and all of it appears to have been in S3^mpathetic connection with the 

 vast subsidence in the water hemisphere. 



Summation and Conclusions 



My paleogeographic studies have confirmed the well-known fact that 

 the vast medial region of the North American continent, while slightly 

 positive, is in reality neutral in regard to sealevel. It is the "nucleus," 

 or "Kratogen," of the continent, taking in the greater part of eastern 

 Canada and most of Greenland (see map, figure 3). This very ancient 

 land, in its rocks and structure, is seemingly in the main of Archeozoic 

 making, but during much of Proterozoic time was still undergoing oro- 

 geny. Since the late Ordovician the neutral region has been a lowland. 



The great neutral area of Canada is continued south westward across 

 the region known as Siouia into greater Mexico. It can therefore be 

 definitely stated that Siouia and especially the Canadian shield have ever 

 since the Cambrian furnished but little clastic sediment to the seas. 

 Western Mexico and Siouia, on the other hand, were during the Mesozoic 

 highlands furnishing sediments in great volume to the adjacent seas. 



