MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
23 
On the other hand, from the facts presented in regard to the intercommunication of subterranean 
streams, caverns, and wells, it may be inferred that all in Grayson county, Kentucky, for example, 
or in the Wyandotte Cave region, belong to one and the same system of subterranean drainage. 
That the Mammoth Cave system of caverns is connected with the Wyandotte system on the north 
side of the Ohio may well be doubted, since there are such radical differences in the faunae of the 
two systems of caves. But the blind fish and crayfish found in wells without doubt enter such 
places from dark, subterranean streams, and sometimes it may happen, as in the case mentioned 
by Mr. Putnam,* that these creatures may occasionally go very near the entrance into partial day¬ 
light. On all these points, however, much is to be learned by future exploration. 
THE GEOLOGICAL AGE OF THE CAVES AND THEIR PRESENT INHABITANTS. 
This topic we have formerly discussed in the American Naturalist (December, 1871,) and we 
then coincided with Professor Cope, “that our true subterranean fauna probably does not date 
farther back than the beginning of the Quaternary, or Post-Pliocene period.” All geological authors 
agree that these caverns have been made by running water. 
It is evident from Wheatley and Cope’s account of the Port Kennedy Cave that there are in 
the Central and Atlantic States two classes of caves ; an older or preglacial and a much more 
recent class, and hence we can be more specific in assigning an age to the caves as we now find 
them. 
It seems quite evident that the fauna represented by the Port Kennedy collection, with its 
remains of the tapir, peccary, and the bones of the Megatherium, Megalonynx, and Mylodon in 
the caves of Virginia, was rendered extinct by the proximity of that region to the glaciers, which 
extended during the height of the glacial epoch into northern New Jersey, Pennsylvania, and 
southern Ohio, Indiana, and Illinois. 
The present caves, whether in existence before the glacial epoch or not, were with little doubt 
reexcavated, enlarged, and assumed their present proportions synchronously with the formation 
of the Niagara gorge, the gorge of the Mississippi, and other river valleys throughout the Northern 
States. The Mammoth and the numerous other caves in Grayson county, Kentucky, must, for 
example, have been excavated by the confluents of the Green River in the higher levels during the 
River Terrace epoch, and long after the melting and disappearance of the ice. After the then great 
rivers had shrivelled to nearly their present size the deeper abysses or pits and channels were cut, 
while the subterranean passages were drained dry simultaneously with the general desiccation 
of the country, until the autumnal, winter, and spring freshets alone sufficed to flood certain of the 
lower passages and galleries which were and now are dry in the summer time. 
It seems, then, fair to assume that the final completion of the caverns, when they became 
ready for occupancy by their present fauna, may not date back more than—to put it into concrete 
figures—from 7,000 to 10,000 years, the time generally held by geologists to be sufficient for the 
cutting of the present river gorge of the Niagara and the Falls of St. Anthony. We may, then, 
put the age of our cave fauna as not much over from 5,000 to 10,000 years before the dawn of 
history, which itself extends back some 5,000 to 6,000 years. 
We think we have given sufficient proof that the greater part of the cave fauna of this country 
was directly derived from the present fauua, with nearly, if not quite, the same limits as it had at 
the time of the Columbian discovery of the country. Before the present cave fauna could have been 
established the late Pliocene or preglacial fauna, with the Megatherium and other gigantic sloths, 
the tapir and peccary, was swept away by the incoming Glacial epoch 5 then the present fauna was 
established, and, as emigration from the south went on, and the emigrants intermingled with 
boreal and antarctic forms, and the cavernous regions became drained and dry—not until then 
(which was obviously but a few thousand years ago) were ojiportunities offered for the establish¬ 
ment of the existing cave assemblage. The biologist, in seeking an explanation of the origin of 
* Mr. Putnam alluded briefly to the other forms of animal and vegetable life in the caves of Kentucky, and 
specially mentioned a cave on the opposite side of the Green River, several miles below the Mammoth Cave, where 
blind fishes and blind crayfishes were obtained very near the entrance by himself, and previously by others, so near 
the entrance that artificial light was not required to see the specimens. (Proc. Bost. Soe. Nat. Hist., xvii., 223.) 
