AND CAVERiSr LIFE IN THE OHIO VALLEY. 359 



the floors. At the end of this series comes the stream which represents the base of the 

 drainage of the country.^ 



With this sketch of the essential elements of structure of the caverns, it now only remains 

 for us to complete our view of their development hy an examination of certain features in 

 their history. In the first place it is important to notice that the development of caverns 

 depends in a great degree on the massiveness of the limestone beds ; when these limestones 

 are thin-bedded, or intershafted at many points with sandstones or clays, the essential con- 

 ditions for the formation of large caverns are wanting. Now whence comes the massive- 

 ness of this limestone ? This feature of massiveness is not uncommon among metamorphic 

 limestones, like those of Carrara, or the limestones of the Cambrian series in this country, but 

 among our unaltered limestones this uniformity is rather peculiar. I am somewhat inclined 

 to attriljute this massiveness to the nature of the organic life which secured their deposi- 

 tion. Beds of molluscous fossils are ver^- apt to be much divided horizontally, while those 

 composed of crinoidal remains are apt to be more soldered together. A possible explanation 

 of this may be found in the fact that crinoid stems evidently remained standing on their 

 roots after the head had died, so that when the stems are planted each a few inches apart, 

 with new ones constantly coming in between, there would be no interruption to the deposit 

 until the crinoidal life was ended. 



The enormous area of crinoidal limestones in Kentucky, at the time of the cai'boniferous 

 limestone, leads ns to suppose that the water was warm, and richly charged with carbonate 

 of lime. No other form of life, not even corals, could take such large quantities of lime 

 from the water over so great an area at the same time. It is impossible to suppose that 

 this deposit was deep water, for the molluscan forms are quite large ; and it is quite as diffi- 

 cult to believe that land was near by, for the amount of silt is not large ; ^et it is required 

 for us to suppose large areas of land feeding the sea with the wash of its limestone rocks, 

 currents bearing the sea water charged with this carbonate of lime, and a perfect immunity 

 from the deposition of sand. 



Age of the Caveexs. 



The fact that there is a complete and very detailed stream topography, or contours 

 formed by running water, on the surflice of the overlying sandstone, and on the uppermost 

 beds of the limestone, shows that the smaller streams did not always run in subterranean 

 ways, but pursued their surface channels until the main rivers had cut well down into the 

 limestone, so there could have been no great system of caverns until this down cutting had 

 brought Green River into the limestone. It is therefore only necessary for us to compute 

 the time which has elapsed since the process began, in order to determine the duration of 

 the cavern sjstem in this section. Data for making this conq^utation in the most satis- 



1 Of the (liap;i-ams, PI. xn, fig. 1 represents the j;cneral D, D. " Sink holes," that in the sandstone beinf unusual 



system of the limestone caves in their fullest development; in that kind of roek. 



fig. 2 the sandstone caverns. Only three sink holes are C, C, C. "Domes" below large " sink holes." 



indicated and only half a dozen chambers. Jn Edmonson D, D. Upper level of caverns being the first formed. 



County alone there are probably over four thousand sink F. Cavern filling with stalactitic deposit, 



holes and over five hundred open caverns. G. Lowest level of caverns opening at level of river. 



A, A. S.andstone above limestone, showing ordinary to- //, //. Masses of pebbles, forming, when put in motion by 



pography. falling water, a powerful cutting engine. 



