756 THE MAMMOTH CAVE AND ITS INHABITANTS. 
ed, the caves of the western and middle States are in lower Car- 
boniferous limestone rocks, though the Port Kennedy cave explored | 
by Wheatley and Copef is in the Potsdam limestone. They could 
not haye been formed under water, but when the land was drained : 
by large rivers. This could not have occurred previous to the Tri- 
assic period. Prof. Dana in his *‘ Manual of Geology” shows that : 
the Triassic continent spread westward from the Atlantic coast “to 
Kansas, and southward to Alabama; for through this great area | 
there are no rocks more recent than the Paleozoic.” ‘Through the 
Mesozoic period [comprising the Triassic, Jurassic, and Creta- | 
ceous periods] North America was in general dry land, and on the 
east it stood a large part of the time above its present level.” 
Though at the close of these periods there was a general extine- 
tion of life, yet this was not probably a sudden (one of months 
and even years), but rather a secular extinction, and there may be 
plants and animals now living on dry land, which are the lineal 
descendants of mesozoic and more remotely of Carboniferous forms 
of life. So our cave animals may possibly be the survivors of Mes- 
ozoic forms of life, just as-we find now living at great depths in 
the sea remnants of Cretaceous life. But frag the recent explora- 
tions in the caves of Europe and this country, especially the Port 
Kennedy cave, with its remarkable assemblage of vertebrates and 
Insects, we are led to believe from the array of facts presented by 
Prof. Cope that our true subterranean fauna probably does not 
date farther back than the beginning of the Quaternary, or Post 
Pliocene, period. We quote his “general observations” in his 
_ article on the Port Kennedy fauna. : 
of the | 
would te 
is cave will be found in the Proceedings 
oo Sy iety, April, 1871. The insects there enumerated 
® robably not come under the head of cave insects, 
