362 ORTMANN — DISTRIBUTION OF DECAPODS [April 3, 



interoceanic connection through the Orinoco valley, discussed 

 above, is not taken account of, and since, as we shall see presently, 

 the relations between Guiana and Brazil and between Guiana and 

 Venezuela are much more complex than v. Ihering assumes. 



Considering the tectonic configuration of South America, we are 

 to mention, in the first place, that the whole eastern part is formed 

 by the so-called Brazilian mass (Suess, 1885, p. 655 ff.) : this is an 

 old Archaic-Paleozoic plateau, which was possibly connected, 

 from very early times up to the Lower Cretaceous (see p. 350), with 

 Africa. Part of this mass is formed by the mountains of Guiana 

 (Suess, 1885, p. 658), and the present valley of the Amazonas is a 

 symmetrical syncline within the old plateau, in the centre of which 

 are Carboniferous beds and, on top of the latter, Upper Cretaceous 

 deposits. Thus the Amazonas valley was apparently land during 

 most of the Mesozoic time, and Guiana was connected with Brazil ; 

 but in the Upper Cretaceous it was a wide sea, the northern and 

 southern shores of which were formed by Paleozoic rocks (Suess, 

 1885, p. 660). This sea extended from the Atlantic westward into 

 the region of the Upper Maranon, in the Cordilleras, and probably 

 connected with the Pacific Ocean (Suess, 1888, p. 683), which is 

 very likely, since the western shore of the old Brazilian mass hardly 

 extended to the eastern foothills of the Cordilleras (in a certain 

 region, the present river Madeira marks the western boundary), and 

 since it is quite sure that the Cordilleras were sea during the 

 Jurassic as well as the larger part of the Cretaceous. This results 

 in an Upper Cretaceous interoceanic connection between the 

 southern Atlantic and the Pacific, which was situated about where 

 the Amazonas valley now is. This Upper Cretaceous strait agrees 

 7viih the sea that separated von Ihering' s Archiplata and Archi- 

 guiana, but it is well to emphasize the fact that it is restricted, as a 

 separating strait, to the Upper Cretaceous period : during previous 

 times, especially the Jurassic and Lower Cretaceous, it did not 

 exist at all, and later it was changed into a bay, as we shall see 

 below. The interoceanic connection during the earlier Cretaceous 

 was not situated here, but went by way of the Orinoco valley (see 

 above, p. 360). The directions of both straits converge to the 

 westward, and it is possible that they actually met, if they coexisted 

 at any time : but generally, we are to maintain that the separation 

 of Central and South America during the Loiver Cretaceous was 

 effected by the Orinoco Strait, and that at this time Guiana was 



