506 E. C. CASE 
limits of “‘Permo-Carboniferous conditions” at every place where 
they are known. 
The sequence in the evidence of the progressive development 
of the red bed westward is broken in two places by the elevation 
at the Cincinnati anticline and at the elevation in Missouri. An 
effort has been made to trace the beds around these elevations, but 
as yet with indifferent success. - The breaks are in part due to the 
effects of erosion removing all traces of Permo-Carboniferous 
deposition and in part to the fact that these lands were elevated 
above the plane of deposition before the climatic migration .had 
reached them. 
An apparent conclusion from the premises here stated is that 
the Permo-Carboniferous vertebrate fauna originated in the eastern 
part of North America and migrated westward. This the author 
is not yet entirely ready to accept, and yet he is strongly impelled 
toward that conclusion by the facts that the earliest known reptile 
was discovered in the Allegheny series, at Linton, Ohio; that typical 
Permo-Carboniferous vertebrates appeared in middle Conemaugh 
time in Pennsylvania and West Virginia, and that typical Pelyco- - 
saurs occur in the red beds of Prince Edward Island at a strati- 
graphic level much lower than those of Oklahoma and Texas. 
The theses of this paper are: 
1. That environment is the determinant factor in the develop- 
ment and spread of a fauna. 
2. That an environment favorable to a certain group may 
develop and migrate, involving different levels of one or more 
geological epochs. 
3. That a fauna or flora may be correlated as belonging within 
the limits of such an environment independent of stratigraphic 
levels. 
| 4. That the limits of such an environment may be detected by 
various lines of inorganic evidence. In the case of the development 
and spread of ‘“Permo-Carboniferous conditions’”’ the effect of 
climate furnishes the observable limits. 
Further evidence for the statements made in this paper and more 
extended treatment of the subject will be given in a monograph of 
the Carnegie Institution of Washington dealing with the environ- 
ment of life in the late Paleozoic. 
