340 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. 
