340 J. W. Judd—On Volcanos. 



But as a matter of fact a number of new forces would be called 

 into operation by the enormous depression and accumulation of sedi- 

 ments along these geosynclinal lines. At a depth of 40,000 feet, 

 taking the average increase of temperature as determined in mines, 

 bore-holes, etc., as our guide, we may infer the existence of tempera- 

 ture capable of producing a decided red heat, and doubtless sufficient 

 to permit of the imprisoned water and other substances, acting during 

 enormous periods, effecting the most striking metamorphio changes. 

 But this is not all. The softening plastic mass thus produced, 

 yielding to the enormous lateral pressure, would be folded and 

 crushed together, and, as has been shown by Sorby and Hunt, the 

 mechanical force where opposed might be transformed into chemical ; 

 and thus fresh energy would be communicated to those operations 

 whereby new crystalline products were being formed from the 

 sedimentary masses. Still another cause must be added in the heat 

 produced by the transformation of the crushing forces, as shown by 

 Wurtz, Vose, and Mallet. From all these causes combined, the 

 thickened mass of sediments of the geosynclinal, especially in their 

 lower portion, would be folded and crumpled and at the same time 

 subjected to such an amount of internal chemical action, as would 

 permit of the elements of which they are composed arranging them- 

 selves into crystalline minerals, according to their several affinities, 

 under the peculiar conditions of pressure and temperature. 



This breaking up of the geosynclinal, resulting from continued 

 subsidence along a line of weakness, has sometimes been spoken of 

 as resulting in a catastrophe, when the mass, weakened by accessions 

 of heat, first began to collapse. But it is perhaps very doubtful if 

 any such marked cataclysmic effect would ever be produced. It is 

 at least equally allowable to suppose, that as each inferior stratum 

 came v/ithin the influence of the metamorphic action, and, acquiring 

 plasticity, yielded to the latera,l or tangential strain, it would become 

 folded on itself, and thereby tend to neutralize the subsiding move- 

 ment of the overlying masses. Thus there would be set up two 

 opposing tendencies in the great thickened mass, and in the end the 

 upward strain resulting from the folding together and crumpling 

 of the lower strata would gradually neutralize and finally overcome 

 the downward bending, the cause of the great subsidence, which was 

 the first effect of the lateral pressure. 



When this point was arrived at, the long-continued downward 

 movement in the Alpine region would be brought to a close, and in 

 the end reversed. And as a fact we find during the period of the 

 Oligocene the evidence of just such a pause and gradual reversal in 

 the movements which had been going on in the Alpine and 

 surrounding districts. The accumulations of thick masses of marine 

 strata, indicative usually of a considerable depth of water, gradually 

 ceased ; littoral, brackish-water, and finally lacustrine and terrestrial 

 deposits succeeding them. 'J'hat the subsiding movements were 

 still locally maintained, while the general tendency was towards a 

 movement of elevation, is shown by the great thickness of terrestrial, 

 lacustrine or estuarine deposits accumulated at certain points, and 



