Permian Formation of Texas. 127 
IS sufficiently marked to make it conveniently distinguishable by the 
eye. Besides this, the mesozoic element which has been shown to 
exist among the invertebrates of the Permian of Texas may be 
properly regarded as holding an opposite relation to the Palaeozoic 
element, and thus to suggest a balance of palaeontological evidence 
in favor of the Permian age of that formation." 
The present state of our knowledge, or warranted opinion, as to 
the existence of the Permian formation in North America may be 
summed up briefly as follows : — 
Although the two earlier groups of the Carboniferous system, 
namely, the Lower Carboniferous and Coal-measures are as clearly 
recognizable in the region traversed by the Mississippi river as they 
are in Europe, in many parts of this continent where Carboniferous 
strata are largely developed no distinctive recognition of either of 
those groups, or of the Permian, is practicable. 
In those regions where the Coal-measures or their equivalent 
strata are recognizable, certain strata are sometimes found resting 
upon them which have been referred to the Permian ; but those 
strata are as a rule, not distinctly separable from the Coal-measures 
upon either stratigraphical, or palaeontological ground. That is, no 
distinct stratigraphical plane of demarkation between the Coal- 
measures and the reputed Permian is observable. Besides this, 
many of the common Coal-measure species range up into those Per- 
mian strata, and many acknowledged Permian types, according to 
the European standard, occur in the unquestioned Coal-measure 
strata beneath them. 
The upper limit of the Carboniferous system and the lower limit 
of the Trias, have never been clearly recognized upon this conti- 
nent, and it is therefore not yet known that either of these systems 
are here at any point complete in that respect. But the upper lim- 
it of the Carboniferous system is known to be incomplete at most 
Notwithstanding the mezozoic character of some of the fossils 
found in the reputed or true Permian strata the relationship of all 
these strata, both palseontologically and stratigraphically, is far 
more intimate with the Carboniferous than with the Trias. 
of X\ii Ammonites par keH oi lleilprin in the underlying Texan Coal-measures, 
and by the presence of similar types beneath the Permian in certain parts of the 
old world. Still, such forms as Ptychites cumminsi may properly be regarded as 
mmediate harbingers of the Mesozoic age. 
