J, W. Judd — On Volcanos. 339 



numerous other observers. Vast masses of limestone, sometimes 

 thousands of feet in thickness, and not unfrequently wholly or in part 

 converted into dolomite, stand in the midst of the sedimentary 

 deposits of different age in the Alpine regions ; and the nature of 

 the organic remains of which these are built up leaves no room for 

 doubt that they represent the enormous coral-reefs of this old period 

 of subsidence.^ At the present day, denudation having swept from 

 their sides the masses of sediment by which they were surrounded 

 and embedded, these calcareous and often dolomitized pinnacles 

 stand in isolated grandeur, constituting some of the most striking 

 scenery of our continent. 



To refer once more to the results of Darwin's researches on the 

 changes taking place on the globe at the present day, we may point 

 out that he has shown how areas of depression are characterized by 

 the non-appearance of volcanic action within them ; and it is interest- 

 ing to find that, during the prolonged periods of depression in the 

 Alpine area, we have very few, if any, indications of the occurrence 

 of volcanic outbursts within it. In the limestone area of the Tyrol 

 and Salzkammergut, it is true that a few intrusive masses of gabbro, 

 serpentine and other rocks have been noticed ; but they are in every 

 instance, so far as I am aware, unaccompanied by any appearances 

 which would indicate that these igneous masses had ever reached the 

 surface and produced volcanic action there. Indeed, it may be 

 asserted as a matter of fact that the Mesozoic period was, throughout 

 Central Europe, marked by an almost total cessation of volcanic 

 activity ; although in the eastern portions of Europe, as in the 

 Carpathians and Greece, small and scattered igneous outbursts would 

 appear to have taken place in the Liassic and Cretaceous periods. 



Accordingto Dana, the "geosynclinal" ordownward bending of the 

 earth's crust, the formation of which was the first stage in the origin 

 of the Appalachian chain, began in or before the Cambrian period, 

 and did not close till after the completion of the Carboniferous ; 

 and during this interval a mass of strata, which at its thickest part 

 could not have been less than 40,000 feet or eight miles in thickness, 

 was formed. Similarly the " geosynclinal " of the Alps, of which 

 the formation appears to have been going on during the whole 

 interval between the commencement of the Trias and the end of the 

 Nummulitic, seems to have led to the accumulation of a mass of 

 strata having an aggregate thickness which probably is scarcely, if 

 at all, inferior to that exposed in the Appalachians. 



It is evident that this downward bending of the crust, of which 

 we have so many clear examples in mountain ranges situated at 

 different parts of the earth's surface, could not go on indefinitely. 

 Even if no fresh causes were brought into action, the time must 

 come when the lateral thrusts, which had produced so striking an 

 effect in the downward fold along the line of weakness, must have 

 given rise to a crumpling or crushing together of the rock masses 

 along this same line, rather than to its simple depression in a down- 

 ward curve. 



^ See Review of Gilbert's and Churchill's Dolomite Mountains (by the late Dr. 

 S. P. Woodward), Geol. Mag. 1864, Vol I. p. 40.— Edit. Geol. Mag. 



