26 Mr Mohs' Summary of Geognostical Phenomena. 



ignited masses raised up, amount to quantities equal to the vol- 

 canic rocks, and even surpassing them, as we have seen above. 

 But nowhere on the surface of the earth, or in the atmosphere, 

 are such immense masses found. If the defenders of such a 

 hypothesis were to suppose that in former times the propor- 

 tion of oxygen in the atmospheric air was greater than now, 

 the possibility of such a supposition cannot be denied without 

 hesitation ; however, it may be remarked, that there are other 

 grounds for inferring the opposite opinion. 



The further details I have to offer on the subject must, 

 however, be reserved for publication in a future number of this 

 Journal. 



Summary of the most important Geognostical Phenomena with 

 which it is necessary to be acquainted in Preliminary Mining 

 Operations. By the late Frederick Mohs, Councillor of 

 Mines at Vienna, and Knight of the Royal Saxon Order of 

 Civil Merit, &c. (Concluded from Vol. xxix. p. 21.) 



Repositories of Simultaneous and of Posterior Formation. — It 

 is now time for us to direct our attention for a short space 

 to the object of the search, to the manner in which reposi- 

 tories of useful minerals are contained in the various rocks 

 which have been considered, and to their different relations. 

 Two kinds of these repositories are generally distinguished, of 

 which the one is assumed to be of simultaneous formation* with 

 the including mountain-mass, and the other is regarded as of 

 posterior formation. t To the first belong beds, and lying 

 masses (liegende Stocke), and under the other are included 

 veins of a great variety of descriptions. We can easily judge 

 of this classification, when we find that geognosts, and with 

 reason too, speak of contemporaneous veins, that is, of such 

 as are of simultaneous origin with the mountain-masses. A 

 contemporaneous vein is a repository which has been produced 

 as a vein at a later period than the rock, and which, neverthe- 

 less, as a contemporaneous vein, is of simultaneous formation. 

 As this is a contradiction, and as the contemporaneous veins 



"-'•' See Vol. xxix. of the Journal, p. 4 . 



t DAubuisson, Traite' de Geognosie. Ire edit. t. ii. 



