72 ; _ Natural History of Volcanos and Earthquakes. 
so sails 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. Meteori¢ 
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 stich 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 columbs are sometimes traversed and 
disjointed by traverse clefts. ‘The surfaces of separation (Ab-_ 
sonderungs F'lachen) 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 bécties condenagl 
again, and resume the same course or circulation. 
Since the voleanic 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 cours? 
designated in the preceding remarks. These two last cases see™ 
to be the most usual, as the circumstances above explained, prov® 
viz., that thermal springs most frequently present themselves be 
tween the unstratified and stratified rocks. I have imagined thé 
