288 ANNUAL KEPOET SMITHSONIAN INSTITUTION, 192 8 



Atlantic type, and takes it as an indication of cross fracturing and 

 foundering of portions of the continents. in later geologic ages. 



The rift valleys of equatorial Africa and the deep narrow basins 

 in the western United States, such as Death Valley, are known to be 

 sunken blocks founded by fractures. The Red Sea, the Gulf of Cali- 

 fornia, and Davis Strait bear the marks on their borders of being 

 similar but larger examples. These troughs therefore appear to be 

 grabens, formed by recent sinking of blocks below sea level, and the 

 adjacent lands of ancient rocks still stand high because they are not 

 yet reduced by erosion. 



From these faulted eml)ayments of the sea it is but a step to certain 

 islands which appear to be ancient remnants of land completely sur- 

 rounded by the spreading ocean basins. Such upstanding pedestals 

 are the " liorsts " of Suess. Madagascar, off the east coast of Africa, 

 is the most striking of these, consisting of a table-land of ancient 

 crystalline rocks stepping up in successive levels and partially skirted 

 by a fringe of Cretaceous and younger strata. Its structure suggests 

 that it has been isolated from Africa and from India by fragmenta- 

 tion which began to be evident in Cretaceous time. In further sup- 

 port of this conclusion is its archaic mammalian fauna, preserved 

 there as in an asylum, and protected by the barrier of the ocean 

 from the predacious higher mammals of the adjacent continents. 



The ^gean Sea appears to be a region breaking up and founder- 

 ing in the present geologic period. The mountain structures are cut 

 across and terminated by great faults that bound the sunken areas. 

 It is a region of present geologic movements and consequent violent 

 earthquakes. Deep, unfilled pockets exist in the adjacent seas. Fi- 

 nally, on the island of Kos there are river deposits which were laid 

 down when it was surrounded by higher land. 



Passing to more ancient times, the Paleozoic marine sediments of 

 Great Britain seem to have derived their materials chiefly from a 

 land situated to the northwest, which Hull called Atlantis. On the 

 other side of the Atlantic, the thick formations of the Appalachian 

 system came from the vanished Paleozoic land to the east which has 

 been named Acadia, and which formed the northern part of the 

 greater land of Appalachia. The writer has calculated elsewhere ^^ 

 the volume of sediment deposited in Upper Devonian time and finds 

 it so great that the land supplying it would seem to have necessarily 

 extended out into what is now the ocean basin. 



Let us turn next to the nature of the biologic evidence. Paleon- 

 tologists have pursued their studies of the ancient marine deposits so 

 far that they are now able to tell whether the entombed fauna in any 



" J. Barren, The Upper Devonian Delta of the Appalachian Geosyncllne. Amer. Journ. 

 Sci., 37, 225-253. 1914. 



