34o THE POPULAR SCIENCE MONTHLY 



at the opening of the Devonian time. It seems to have come west- 

 ward from a dispersion area in Africa and it evidently disseminated 

 itself without interruption of continuity from the strands which now, 

 as the Bokkeveld beds of Cape Colony, constitute the only evidence 

 of marine life in the South African Paleozoic, to those of the Falkland 

 Islands, two far distant regions which have much more of organic 

 content in common than do the Falklands and the nearer regions of 

 Parana, Argentina and Bolivia. 



This fauna with its special and peculiar features is, however, spread 

 through Bolivia, western Argentina, southern Brazil, including Parana 

 and as far north as Matto Grosso, thence eastward by way of the Falk- 

 lands to South Africa. From the boreal strands of the period it was 

 separated by a barrier, often narrow and constituted only of deeper 

 water, so that of the boreal Devonian we find no evidence much south 

 of the equator in Brazil nor of the austral Devonian north of that line. 

 This barrier I believe to have been overpassed at times during the early 

 part of the Devonian by species which are of wider distribution south 

 and north but these passages seem to have become rarer as time passed 

 and as more complete geographic isolation was effected. 



There are many evidences in this southern fauna that the land 

 bridge was accompanied by insular strands which are evidenced by 

 varying percentages in community of species and by bathymetrical 

 variations. Apart from these possible island masses, there was clearly 

 a Devonian land bridge extending from South Africa to the Falklands, 

 westward into Argentina and northward into Bolivia, embracing also 

 as continental or island lands parts of the states of Parana, Matto 

 Grosso and even of Para. 



By virtue of the evident derivation of the fauna of this time from 

 the east along newly forming strands which were, throughout the 

 period of the Devonian, kept asunder from the Atlantic-European 

 lands at the north, and by its further development under conditions 

 of isolation, the fauna presents fundamental contrasts to any develop- 

 ment of the Devonian elsewhere in the world. It is in itself a unit and 

 a unit also in relation to the sediments in which it is involved. There 

 is no earlier Devonian in this southern region nor is there any later 

 Devonian, for wherever the succession has been determined this austral 

 fauna, bearing no evidence in itself of a later time stamp than early 

 Devonian, is overlain by Carboniferous deposits without demonstrated 

 unconformities between. Deposits and faunas which at the north we 

 are accustomed to regard as of later Devonian age, are absent at the 

 south, either because this austral land was broadly above the sea dur- 

 ing these stages and its strands now lie buried or, as seems much more 

 probable, this sedimentation represents the total Devonian sedimenta- 

 tion and this fauna the total Devonian fauna at the south. 



