THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE II. VOL. III. 



No. XII.— DECEMBER, 1876. 



oi^ia-i35r-A.ij .A^i^TicXiES. 



I. — Contributions to the Study of Yoloanos. — Second Series. 



By John W. Judd, F.G.S., 

 Professor of Geology in tlie Eoyal School of Mines. 



On the Yolcanic Outbursts which accompanied and followed 

 THE Formation of the Alpine System. 



OF the amount of vertical movement which took place in the great 

 mountain axis of the Eastern continent, subsequently to the de- 

 position of the Eocene strata, the following facts afford sufficient 

 proof. The marine Nummulitic rocks, besides constituting very large 

 portions of the flanks of this vast mountain axis, and of its connected 

 chains, such as the Pyrenees, the Carpathians, and the Caucasus, 

 form the actual summits of such grand Alpine peaks as the Diablerets, 

 and the Dent du Midi, rising to the heights of 10,670 and 10,531 

 respectively above the sea-level ; while in Western Thibet the same 

 Eocene strata are seen raised to an elevation of no less than 16,500 

 feet above the sea. 



But even these measures, vast as they are, supply us with a very 

 inadequate conception of the amount of disturbance to which the 

 district in question has been subjected during the post-Eocene epoch. 

 In order fairly to realize the all-powerful action of the subterranean 

 forces at work in the later Tertiary periods, we must examine the 

 enormous beds of sand and pebbles constituting the Lower, Middle, 

 and Upper Miocene of the Western Alps, and presentiug an aggre- 

 gate thickness in places of between 7000 and 8000 feet — telling, as 

 they do most unmistakably, of local subsidences of not less than that 

 amount with subsequent re-elevations to an equal extent. 



It is only, however, when we come to examine the constantly 

 highly inclined, the frequently vertical, and sometimes greatly con- 

 torted and even inverted positions of these Miocene rocks, that we 

 are fairly impressed with the magnitude of those earth-movements, 

 of which these districts were the scene during the second half of the 

 Tertiary epoch. These facts, of which we find such striking evidence 

 in Switzerland and the Western Alps, are equally patent to the 

 geological student in Eastern Europe. In the Tsil Thai on the 

 flanks of the Transylvanian Alps, for example, a portion of a vast 

 deposit of Oligocene strata, consisting of clays, sandstones and coals, 

 with a thickness of between 2000 and 3000 feet, has been bent into 

 a sharp synclinal fold, and this fragment has alone survived the 



DECADE II. — VOL. III. — NO. XII. 34 



