110 Permian Formation of Texas. 
Mr. Cummins for a large part of the facts upon which the follow- 
ing description of it is based. This is especially true with regard 
to the extent of the area which it occupies. 
In Texas this formation occupies an area, many hundred square 
miles in extent, which constitutes the western part of the southern 
extremity of the great central paleozoic region of the continent. 
The southern boundary of this area is not now definitely known, 
but it lies at least as far south as the Concho river. Its eastern 
boundary may be approximately designated as extending from Red 
river to the Colorado through Clay, Young, Shackelford, Callahan 
and Runnels counties ; and its western border as extending from 
the Canadian river to the Concho through Hemphill, Wheeler, Don- 
ley, Briscoe, Motley, Dickens, Garza, Borden and Howard counties. 
The formation is known to extend northward far within the Indian 
Territory, but in this article special reference is made only to that 
portion of it which is found in Texas ; and the description which 
is herein given is drawn mainly from observations made in Baylor, 
Archer and other contiguous counties. 
This formation rests directly and conformably upon another se- 
ries of strata in which a characteristic Coal-measure fauna prevails 
but which IS not now known to include any fossils of mesozoic types, 
if we except the Ammonites pay-keri oi Heilprin, which he states was 
obtained from Carboniferous strata in Wise county .^^ Notwith- 
standing the mesozoic character of a part of the moUuscan fauna 
of the upper formation, the preponderance of evidence makes it 
necessary to regard it as belonging to the great Carboniferous sys- 
tem, and as constituting an upper member of it. For these and 
other reasons yet to be stated I have little or no hesitancy in desig- 
nating this Texan formation as Permian, as Prof. Cope has done ; 
but I shall briefly discuss in following paragraphs the propriety of 
the use of that name for all of the North American strata to which 
it has been applied. 
The Texas Permian is distinguishable in general aspect and 
in lithological character from the formation which underlies it and 
which represents at least a large part of the Coal-measure series 
as the latter is known in the Upper Mississippi Valley. And ye^ 
the Permian strata blend so gradually with those of the Coal-meas- 
ures beneath, and with the gypsum-bearing beds, above that it is 
difificult to designate a plane of demarkation in either case. 
^ Proc. Acad. Nat. Sci. Philad. , Vol, XXXVI, pp. 53-55. 
