AND CAVERN LIFE OF THE OHIO VALLEY. 361 



verly beds, and possibly over the Cincinnati series as -well. If -we assume that one foot 

 of beds disappears every six thousand 3'ears, then we must suppose that several thousand 

 feet of strata have been removed from the top of the Cincinnati axis, unless we consiiler 

 that this axis has been repeatedly under Avater since tlie time of its elevation. My own 

 oj)inion is that this axis has not been constantly aljovc the water line, but that it has been 

 subjected to alternating elevation and subsidence ever since the calciferous sandstone was 

 formed. During the formation of the subcarboniferous limestone it Avas probably elevated, 

 inasmuch as this limestone seems both on the east and Avest to groAV thinner as Ave approach 

 it. During the carboniferous period, or the time Avhen the true coal beds Avere Ijcing laid 

 doAvn it seems more likely that it Avas again, from time to time, submerged. These coal 

 beds, or some later formation, must have coA'ered it and furnished materials for subsequent 

 wear. If this view be correct, then Ave cannot, look for a long succession of ca\'es while the 

 carboniferous limestone AA'as Avearing away from its position a thousand feet or more aboA'e 

 the top of the Cincinnati axis. 



On the Avhole, it seems prol)able that Avhile some caverns may have existed in the Missis- 

 sippi valley long before the tertiary period, their great development and the consequent 

 chances of organic life finding its Avay into cavern conditions is a very recent event. 



In this connection there is a question of considerable moment to be discussed. It is evi- 

 dent that the extension of glacial conditions over any region must absolutely arrest the 

 succession of development of any caverii species. To them migration must be regarded as 

 impossiljle. The temperature brought by ice, even if Ave can suppose that it did not fdl 

 the caA'erns ; the exclusion of supplies of organic matter from the surface, and the inter- 

 ruption of drainage, must make the continuance of this life impossiljle. The question 

 therefore arises Avhether the last glacial period extended its action over this region. On 

 that point I can give a very decided negative answer. A most careful search has flailed to 

 show the slightest trace of glacial action on this region. I am inclined to think it likely 

 that some glacial periods anterior to the tertiary ma}" liaA'e extended their ice sheet as far 

 south as this, but am quite satisfied that the ice jjeriods Avhich have left their distinct record 

 in the north, never operated here.^ Inasmuch, hoAvever, as the southern border of the ice 

 sheet Avas not over two hundred miles to the north, it is evident that the most important 

 general effects on climate must liaA^e been produced, the species now living here must have 

 been driA'en further south by many hundred miles. It uuist, in fact, have brought a boreal, 

 if not an arctic, fauna into their region. When Ave consider the essentially close relation 

 between the life within and the life without the ca\'es, we Ijocome convinced that the cavern 

 species are derived from the present fauna, and could not have been the descendants of an 

 arctic assemblage of species. In the case of the Astacida?, for instance, Ave must suppose 

 either of two things, that the cavern form descended from the outer form l^efore the gla- 

 cial period, or after that time. In the latter case Ave are entitled to suppose that the outside 

 species migrated southward during the glacial period, and returned after its close. 



Considering the Avhole relations of the species fouiul Avithout and within the caverns 

 about the Mammoth Cave, Ave are led to the conclusion that tlie dozen cavei-n forms Avhich 



'In .a succeeding memoir of this porifs 1 shall endeavor to County, an asseml)hige of hfc at the close of tlie glacial 

 show that we had at Big Bone Lick, in Kentucky, a locality period distinctly indicating arctic conditions; this [loint be- 

 about one hundred miles north of the Jlanunotll Cave, but ing about tlie northernmost station for plants and animals 

 not more than forty miles to the north of the caves of Carter doring the fullest extension of the ice sheet. 



MEMOIRS EOST. SOC. ^AT. UIST. VOL. II. 91 



