MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 23 



On the other haud, from the tacts 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 faunas of the 

 two systems of caves. But the blind fish aud crayfish found in wells without doubt enter such 

 places from dark, subterranean streams, and sometimes it may happen, as in the ca'se 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 OP 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 aud 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 boues 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, aud Illinois. 



The present caves, whether in existence before the glacial epoch or not, were with little doubt 

 reexcavated, enlarged, aud 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 conflueuts of the Green River in the higher levels during the 

 River Terrace epoch, aud long after the melting and disappearance of the ice. After the then great 

 rivers had shrivelled to uearly 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, aud 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 fauna, with nearly, if not quite, the same limits as it had at 

 the time of the Columbian discovery of the couutry. 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 ; then the present fauua 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 opportunities 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, aud 

 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 n< ar the entrance by himself, and previously by others, so near 

 the entrance that artificial li;.;hr was not required to see the specimens. (Proc. Bost. Soc. Nat. Hist., xvii., 223.) 



