358 ORTMANX — DISTRIBUTION OF DECAPODS [Aprils, 



sediments on the Pacific side contain the same fossils as the corre- 

 sponding ones on the Caribbean side, which is an important addi- 

 tion to Hill's observations. 



Between these depressions of the isthmian region, filled out by 

 older Tertiary deposits, there are Archaic rocks at various places ; 

 we know of such not only from Guatemala and Honduras, but also 

 from northern Nicaragua (Hayes), Costa Rica (Hill, Hayes), and 

 even farther east, beyond the Panama canal, in the Cordilleras of 

 San Bias. Thus it seems that the present isthmus, from Nicaragua 

 to Colombia, consisted during the older Tertiary of a series of 

 islands separated by ocean straits. 



According to the unanimous opinion of Hill, Hayes, Bertrand 

 and Zucher and others, these straits (Nicaragua and Panama) 

 became dry in the Middle Tertiary, i.e., in the Miocene, and, con- 

 sequently, the cofinection of North and South America was then 

 established. 



Although this Eocene and Oligocene communication of the 

 oceans is admitted by Hill, he is inclined to minimize its import- 

 ance. Moreover, he assumes (1898, p. 263) that to the southward 

 and westward, toward the Pacific, a large land mass must have 

 existed, from which the material of the marine deposits of the 

 isthmus was derived, and, further, he believes that this land mass 

 chiefly extended in a north-southerly direction, probably connect- 

 ing North and South America. I think we do not need this land, 

 and even if we accept its existence,^ it hardly formed, in the earlier 

 Tertiary, a connection of the Americas. Be that as it may, the 

 insular elevations of the isthmus, and the masses of old rocks to the 

 north of it, in Nicaragua, Guatemala, Honduras, and in the 

 supposed connecting land with Jamaica and Cuba (see above, p. 347), 

 were in our opinion sufficient to furnish material for those Old Ter- 

 tiary sediments in the isthmian region."' On the other hand, any 



1 Since we need, as I naost emphatically believe, a connection with Galapagos 

 Islands; this subject,, however, is outside of the present question. 



2 Hill himself (1898, p. 263) discusses the idea that the land to the north of the 

 isthmus may have furnished the material, but dismisses it, since here "we are 

 confronted by great depths." Now, in my opinion, great depths are no funda- 

 mental objection, and just in this case the character of the sea bottom in the 

 region between Honduras, Jamaica, Cuba and Hayti indicates that important 

 disturbances have occurred here, and, in the first place, the deep submarine rift 

 valley, known as " Bartlett deep," may be of a very recent age. 



