The kSeope of PaleoutoUxjy.- — Willi ams. 167 
New York soutliwestwaixi across Peuusylvania, Ohio and Ken- 
tucky, we gradually lose the separate members, and black shales 
become conspicuous in their places, and in Tennessee there is but 
a thin black shale to represent this whole interval, and in northern 
Alabama scarcely anything separates the Silurian (in some cases 
lower Silurian), from the Carlioniferous resting unconformably or 
even conformabl}' upon it. Similar conditions are seen in north- 
ern Arkansas, where, about the Ozark uplift, the erosion of the 
Silurian terrane is such that at the corner of Illinois, Helderl)erg, 
Oriskan}' and even traces of Hamilton are left in place, while 
further west, the latest is Helderberg, or Niagara, or Trenton, 
and at extreme points magnesian limestone was the surface rock 
when the black shale was deposited, to be immediately' followed 
by t3'pical Carboniferous fossils. 
In Texas we find a similar cutting out of the D^'vouian, and 
more or less of the upper Silurian and the Carboniferous follow- 
ing the interval. 
These facts point to an elevation sutticient to occasion extensive 
erosion toward the southwest, followed by depression, which gave 
occasion for the deposit of the black shale over extensive areas. 
If we are correct in tracing with Ulrich his Bolivian Devonian 
fauna to South Africa and recognizing it in the lower and middle 
Devonian faunas of the Appalachian area of North America, and 
in inferring, as I have suggested, that the change in fauna at the 
close of the Hamilton in New York was associated with the ar- 
rival of the Cuboides fauna into the Appalachian region, and thus 
that the upper Devonian is distinctly a European- Asiatic fauna 
and connected with it across the Pacific down the Mackenzie 
region, it is evident that the time of the change of these faunas 
corresponds with the time of the geologic events in the southern 
central part of the United States, above referred to. The eleva- 
tion which occasioned the erosion did not take place till the Ham- 
ilton period, and the depression and deposit of Black shales 
followed the incursion of the new fauna, or was. in part, contem- 
poraneous with it. 
The erosion ceased and the deposition b?gan in the south later 
than in the north, as is indicated by tlie fuller rei)resentations of 
the separate deposits at the north than at the south, also b\' the 
smaller amount of the deposits, as indicated 1)V the gradually 
thinning black shale on passing from Ohio across Kentucky to 
