S80 Prof. Bischof on the Natural History of 



deep into the interior. It must, however, be observed, that be- 

 tween these two cases a wide difference exists. In regions 

 where volcanic action still manifests itself, clefts can with ease 

 extend in masses which are of a boiling heat or even hotter. 

 Meteoric water penetrating these clefts will be converted into 

 vapour and exhaled. Were, however, such a phenomenon to 

 shew itself in regions where the increase of temperature follows 

 the progression, which we have found it to do in accessible 

 depths, then must such clefts extend perpendicularly to a depth 

 of about 8280 feet in our country. But are any rocks, even ' 

 the unstratified masses, traversed by continuous clefts of so 

 great a depth ? In granite the prismatic separation is very 

 frequent. The columnar structure is most distinct in basalt, 

 aphanite, and all dense and homogeneous rocks. The columns 

 are sometimes traversed and disjointed by traverse clefts. The 

 surfaces of separation (Absonderungs Flachen) in the smaller 

 masses, always lie perpendicularly on the adjacent ones, as do 

 also the columns, when present. Let us assume that such a 

 jointed separation extends to the requisite depth, and that me- 

 teoric water penetrates so far, and then it will certainly rise 

 converted into steam ; when, however, it attains the higher 

 colder regions, it will become condensed again, and resume the 

 same course or circulation. 



Since the volcanic masses, when thrown up, form, generally, 

 the greatest heights, we must look in them for the compressing 

 columns of water, which render the rising of the springs possi- 

 ble. The possibility of such a case is conceivable, when the 

 surface of the unstratified rock is inclined in one or more direc- 

 tions, and the columnar separations are jointed by transverse 

 clefts. It is, however, even then, possible only when the trans- 

 verse clefts have no continuation outwards, for in this case the 

 water will take a side course, and either issue on the slope of 

 the rocks as springs, or, if raised strata exist, it will take the 

 course designated in the preceding remarks. These two last 

 cases seem to be the most usual, as the circumstances above ex- 

 plained prove, viz., that thermal springs most frequently pre- 

 sent themselves between the unstratified and stratified rocks. 

 I have imagined the last case, in order to exhibit the possibility 

 of hot springs rising in the Alps, when water descends from 



