102 ANNALS NEW YORK ACADEMY OF SCIENCES 



tralian realm have never been found in the whole geological series of the 

 continental shelves. Also, the great number of shark teeth found in 

 abysmal depths indicate vast time for deposition. Until all such data 

 and the theory of isostacy have been satisfactorily accounted for, it ap- 

 pears to be useless to continue hypothesizing land-bridges. At the present 

 stage of our knowledge, we do not need an Antarctic land-bridge, but we 

 do need both dynamical data and more careful field work in northern 

 South America and southern Asia before we can definitely settle the 

 distribution of mammals. 46 



Summary 



We have seen from the location of the Archean and early Paleozoic 

 rocks that about the present outline of South America has always existed 

 and that the lines of weakness and strength in its crust are usually par- 

 allel to the coasts. Hence, the invasions of the seas have, in most cases, 

 been in a general southern-northern direction and not east-west. The 

 location of the deposits left by the invasions of the sea has forced us to 

 deny the existence of Archiguiana, Archamazonia and Archiplata as 

 maintained by some of the exponents of the Archhelenis theory. 



The outlines of the Piano Alto, which was deposited in a continental 

 Permian inland basin, has been given, and the general dip of its surface, 

 its lack of past Paleozoic marine deposits, location of surrounding 

 Archean mountains and marine sediments and the Tertiary rise of the 

 Andes indicate the reversal of the Amazon during the later half of the" 

 Tertiary epoch. The eastward movement of the mouth of Rio Negro and 

 the single channel of the Amazon in region of Obidos, where remains of 

 the Piano Alto approach the river, indicate that this is near the old 

 divide which has been washed away. The unique marine or brackish 

 water fossils of Alto Eio Amazonas apparently lived in an arm of the 

 ocean (East Andean Sea), which probably extended south, lost its con- 

 nection and finally disappeared with the Tertiary rise of the Andes. It 

 was also suggested from the character of the overlap that no great exten- 

 sion of land to the east of the present coast was needed to form the sedi- 

 ments of the Piano Alto and that great altitudes probably existed in 

 eastern Brazil and Guiana during late Paleozoic times. 



The southeastern Brazilian coast appears to be very old and remark- 

 ably stable. It apparently never extended more than about 100 miles to 

 the east of its present location. The fringe of upper Cretaceous deposits 



43 The evidence from the standpoint of the Mammalia for a Tertiary Archhelenis, i. e., 

 a connection between South . America and Africa, is given in the "Age of Mammals," 

 which shows that such a connection did not exist. 



