72 Natural History of Volcanos and Earthquakes. 



As escapes of steam (fumaroles) show themselves in regions 

 (Tuscany for example) where hot masses have approached the 

 surface of the earth by volcanic activity, one might perhaps be 

 induced to expect evolutions of steam from clefts penetrating deep 

 into the interior. It must, however, be observed, that between 

 these two cases a wide difference exists. In regions where vol- 

 canic 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 vapor and 

 exhaled. Were, however, such a phenomenon to show itself in 

 regions where the increase of temperature follows the progres- 

 sion, 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 i-ocks, 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 (Ab- 

 sonderungs Flachen) in the smaller masses, always lie perpen- 

 dicularly 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 meteoric water penetrates so far, 

 and then it will certainly rise converted into steam ; when, how- 

 ever, 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 direcr 

 tions, and the columtiar 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 coarse 

 designated in the preceding remarks. These two last cases seem 

 to be the most usual, as the circumstances above explained, prove, 

 viz., that thermal springs most frequently present themselves be- 

 tween the unstratified and stratified rocks. I have imagined the 



