SUMMATION AND CONCLUSIONS 207 



Of embayments, there are four. (1) With the vanishing of the Saint 

 I^awrence and Acadian troughs in Devonian time, there appeared in 

 greater Acadia the Northumberland embayment, extending across the 

 Maritime Provinces of Canada and Newfoundland (see maps, figures 10 

 und 11). It endured during the Mississippian and Pennsylvanian 

 periods, the subsidence nowhere exceeding 18,000 feet. The embayment 

 ■ceased with the Permian orogeny. 



(2) Chiefly in Arkansas and Oklahoma, from Upper Cambrian to 

 Middle Pennsylvanian time there was developing the Ouachita embay- 

 ment, an east-west trough connecting more or less directly with the Appa- 

 lachian geos}nQcline (see maps, figures 3 and 6). It subsided markedly 

 •during its earliest existence but more especially during the Pennsylva- 

 nian, since in Arkansas the maximum of depression appears to have been 

 35,000 feet. The trough failed as such with the Pennsylvanian orogeny. 



(3) Another west-east trough was the Sonoran embayment of north- 

 western Mexico, which was more or less closely connected with the Cor- 

 •dilleran geosyncline (see maps, figures 3 and 6). It reappeared in the 

 Upper Cambrian and endured into the Pennsylvanian, during which time 

 the trough sank something like 15,000 feet. 



(4) The fourth of these basins was the Alexandrian embayment of 

 southeastern Alaska, which finally merged with the Pacific geosyncline 

 •during the Pennsylvanian (see map, figure 3). It came into being at 

 least as early as the Lower Ordovician, and during its existence the basin 

 sank not less than 12,000 feet. 



It does not follow that when the geosynclines are in flood the neutral 

 areas are at the same time more or less under water. Frequently the 

 floodings are restricted to the geosyncline, and at other times the Arctic 

 Hoods cover essentially the neutral areas of the continents. In the same 

 way, the Mississippian seas west of the Cincinnati geanticline may be in 

 •evidence when the Appalachian geosyncline is dry. 



It appears from the irregularity of the continental floodings that their 

 presence is primarily due to crustal movements, but it does not at all 

 follow that all are so brought about. The widespread and more or less 

 cosmopolitan faunas of the Upper Cambrian, Middle Ordovician, Silu- 

 rian, Devonian, and late Cretaceous appear to bear out Suess' hypothesis 

 of eustatic (= world wide) higher marine levels, when the continents 

 are base-leveled and the oceans most filled with sediments, causing them 

 to spill widely over the lands. Clearly, every grain of sand displaces just 

 as much water. 



As to the time of origin of the primary geosynclines, we may say that 

 all arose in the Proterozoic (see map, figure 1), and that out of the Cor- 



