302 O^"^ THE ANTIQUITY OF THE CAVERNS 



are related to outer species more or less closely, have been derived from those outer forms 

 since the present assemljhige of life in that district was constituted. This conclusion is the 

 more necessary when we come to consider the asseinljlage of life in the caverns in Indiana, 

 Wvandot Cave, etc. Here we are close to the border of the glacial .sheet, and quite within 

 its inlluence, if not at times actually beneath its bed, yet the relations to the external life 

 are here the same as about the more southern caves. 



On another important point we have much light from the study of cavern life. A num- 

 ber of these cavern forms are found on different sides of the Ohio River. Now it is clearly 

 impossible that these forms could have sprung from a common centre, they must have orig- 

 inated at several points. The blind cray fish, the several insects which are common to the 

 several regions, must have originated in each and all of them. The Ohio River, with its 

 wide intervening non-cavernous valley, would be a very formidable barrier for them to 

 traverse, and we have no right to presume that they passed it. 



If the organic forms inhabiting these caverns had been the product of long continued 

 change, begun in distant geological periods, then we should expect this assemblage of cav- 

 ern species to present something of the same general contrast to the life without the cave 

 that is shown in the forms of any two widely separated geological formations plus the spe- 

 cial changes which come from the peculiar conditions of caverns. What we find, in fact, is 

 a fauna which is singularly like that of the outer world, and wherein every important dif- 

 ference is probal:)ly connected with the peculiar conditions in which it has developed. 

 This absence of all mai-ks of difference, such as would have existed had the connection 

 between the inner and outer life been remote, leads us to no very positive conclusion, 

 though it suggests some interesting possibilities. 



In the first place, if these caverns have been in existence for the greater part of the 

 tertiary period, then, either the insect fauna of their neighborhood has been much what it 

 is at present during the whole time of their existence, or the present assemblage of species 

 belongs to the colonization which has taken place since the last great faunal change. Then 

 if we determine that these cavern species have not long inhabited their present abodes, are 

 we to conclude that some agent, such as glaciation, has killed off the earlier cavern 

 forms, prevented as they are from tlie migrations which save the external species ; or is 

 it that organic forms hc'mg introduced to these unnatural conditions can only survive for a 

 certain time, their generation becoming enfeebled in the coiu'se of ages and passing away, 

 so that whenever the constant supply of recruits from the outer world is broken, the given 

 form quickly perishes ? 



These hypotheses are not proposed as dilemmas, but as hints to an important investiga- 

 tion. Let the life of certain caverns be taken, some from within and some from without 

 the region of glacial action ; then with the certainty that in the one case the life has been in- 

 terrupted by ice action, and the reasonable certainty that no such interruption has befallen 

 the life in tlie other set of caves, we shah be a position, by comparing these assemblages of 

 forms, to come to some opinion on this important question. 



The facts oljservidjle in the case of the cray fish of our caverns, seem to lead us to the 

 conclusion, which in fact seems probable on other grounds, that the cavern species are being 

 continually reinforced by the infusion of fresh blood from tlu' outside. "We find, along with 

 the white and siglitless forms, some that are white but with eyes ; others with eyes and some 

 color; still others that are quite like the external species. It Avould be a great addition to 



