88 Professor Favre on the Geology of the German Tyrol. 



of lime ; 2d, a temperature of about 200° ; 36?, a pressure of 

 15 atmospheres. Now, I believe that these circumstances, 

 by no means complicated, may have been met with in the 

 localities actually occupied by the dolomitic chains of the 

 Tyrol. 1st, It is evident that in the sea, where the fonna- 

 tions composing these chains were deposited, lime existed. 

 No one has ever doubted this fact; besides, the encrinites, 

 oysters (?), and the beautiful corals of the Seisser-Alp, are 

 sufficient to prove it. "With regard to the sulphate of magne- 

 sia, we know that it exists in the waters of the sea ; but I am 

 of opinion that a more considerable quantity than ordinary 

 existed in this sea ; and this is my reason — the pyroxenic 

 tufa, as we have said, is the produce of submarine eruptions, 

 and consequently gases, and, among others, sulphurous 

 acid, which always accompanies volcanic eruptions in great 

 abundance, are more or less dissolved in the water ; they 

 have foi'med different salts with the substances which were 

 present. The rocks which were erupted, being very rich in 

 magnesia, sulphate of magnesia must have been formed solu- 

 ble in twenty parts of cold water, and in much less of boil- 

 ing water, according to Berzelius. This salt is met with in 

 the neighbourhood of existing volcanoes, and readily passes 

 into the state of sulphate of magnesia by the action of the air 

 (Thenard). Thus the presence of a notable quantity of sul- 

 phate of magnesia in this sea is placed beyond doubt. 



2d, A temperature, I have said, of 200° C. was required. 

 Such a tempei-ature assuredly existed at a certain depth 

 in a sea where volcanic eruptions took place, and whose 

 bottom was covered with a greater or less quantity of muddy 

 and sandy substances. 



Zd. A pressure of 15 atmospheres. This condition is 

 found to be exemplified in a sea whose depth is only from 

 150 to 200 yards. It is evident that the sea in which such 

 immense masses -as those forming the dolomitic chains of 

 the Tyrol were deposited, was of a much greater depth. 



We have thus all the conditions required for the formation 

 of dolomite, and which must have been met with in nature, 

 according to the ordinary course of things. 



It may also be remarked, that hydrochloric acid is likewise 



