382 Prof. Bischof on the Natural History of 



been since filled up. This constant vaporization of water, in the 

 middle of the same rock in which the cave is found, shews pretty 

 evidently the cause of the warmth in the latter. 



It is scarcely to be doubted, but that, on closer investigation, 

 the phenomenon of local heat in caves in the limestone rocks, 

 which are fissured to such great depths, would be found to be 

 of more frequent occurrence. The spring of the Orbe in the Jura 

 mountain, formerly mentioned, which is nothing more than the 

 discharge of the lakes situated 680 feet higher in the valley of 

 the JouXy proves, among others, to what a depth the clefts in 

 the limestone rocks descend. 



The whole ridge of the chalk hills of the Teutohurger Wold 

 near Pader born, is fissured to depths exceeding 800 feet, so that, 

 on this whole ridge, either no springs at all, or but a few very 

 scanty ones, are met with, which probably owe their existence 

 to partial beds of marl in the chalk rocks. In three villages 

 which lie on this ridge, there is but one well 80 feet deep. On 

 account of this almost total want of water, these are called the 

 *^' Dry Villages." The cleavage continues in the valleys which 

 traverse these hills, consequently the brooks and rivers which 

 flow through them gradually sink and flow out of the open- 

 ings of these valleys only in the wet season of the year. At 

 the foot of these chalk hills on the other hand, where the fissured 

 limestone is covered by a stratum of marl, a very great num- 

 ber of copious springs issue, several of which form considerable 

 rivers, as the Lippe, Pader, Heder, &c., immediately after their 

 exit. The cleavage of the chalk rocks is doubtless continued 

 in the Quader Sandstein, which lies below and probably is li- 

 mited by the lias [grypMtenhalk) and variegated marl, which 

 follow immediately below the green sand, and which are re- 

 markable for their large strata of clay marl {thonmergel), 

 that are impermeable, unless broken or dislocated by ele- 

 vations. This whole chain of hills, then, from the clay-marl 

 strata to the level of the springs which issue on the western 

 declivity of the Teutohurger Wald, is, therefore, saturated 

 with jjwater like a sponge. Not merely geognostical reasons, 

 but also physical relations, furnish incontestible proofs of 

 the existence of these considerable subterraneous reservoirs of 



