122 Permian Formation of Texas. 
(4) northeastern Kansas and southeastern Nebraska ; (5) South 
Park, Colorado ; (6) isolated portions of New Mexico, Arizona, 
Utah and Western Colorado, and (7) northern Texas and the adja- 
cent part of Indian Territory. 
In all these cases there seems to be no room for doubt that the 
strata in question are not older than the Upper Coal-measures, as 
that formation is distinguishable in North America, but aside from 
their evidently high position in the Carboniferous system, their 
recognition as Permian has been based upon different kinds of evi- 
dence in each case. In the first and second mentioned cases it was 
based wholly upon plant remains ; in the third, upon vertebrate re- 
mains alone ; in the fourth, upon invertebrate remains ; in the fifth. 
upon plants and insects,^ and in the sixth, mainly upon stratigraph- 
ical position. The evidence in favor of the recognition of the 
strata, as constituting a separate formation in the seventh case, is 
presented in this article. 
Two general ideas seem to have prevailed respectively in the 
minds of those who have considered the question of the recognition 
of the Permian in North America. On the one hand, the discovery 
on this continent of remains belonging to generic or other types of 
vertebrate, invertebrate, or plant life, which are respectively similar 
to forms found in the European Permian, have been regarded by 
some authors as surely indicating in each separate case the Permian 
age of the strata containing them, even in the absence of, or without 
regard to, correlated facts, whether paleontological or stratigraph- 
ical. On the other hand, it has been contended that no definite 
recognition of the Permian, even in the first-mentioned cases, ought 
to be made until after due consideration of all obtainable corre- 
lated palaeontological and stratigraphical facts ; and not then, unless 
the preponderance of all that evidence should plainly favor such 
recognition. 
The untenableness of the position indicated in the case first 
stated is shown by the facts mentioned in preceeding paragraphs of 
the occurrence in one and the same stratum of forms which have 
been held to be characteristic of separate geological periods, and 
even of separate ages. It is conspicuously shown in the case of the 
Texan formation, which is specially discussed in this article, be- 
