48 Mr. E. W. Hilgard on some points in 



acceptance by geologists, particularly on the continent of 

 Europe. In its application to the formation of synclinoria 

 especially, the principle works most instructively and satisfac- 

 torily. It can scarcely be doubted that in the first folding of 

 the vertex of a geosynclinal, weakened below by fusing away 

 and heating of the crust and lowest strata, the movements 

 were comparatively localized and rapid, and therefore capable 

 of producing high temperatures, and their results such as we 

 now usually find them along the main axes of elevation of syn- 

 clinoria. But as the resistance along this axis increased by 

 emergence and solidification, the points of yielding (i. e. the 

 folds) would be multiplied, while the absolute amount of motion 

 transformable into heat would be diminished in each. Hence 

 the decrease in general of metamorphic effects as we recede 

 from the main axis. And yet it is perfectly easy to conceive 

 of large local exceptions to the general rule (such as we actu- 

 ally observe), on the basis of greater resistance in perhaps a 

 localized stratum of a lateral fold, yet so situated that it could 

 not successfully resist the influence of an advantage of leverage 

 causing a rapid deformation. It is even predicable that under 

 such circumstances sudden breaks and crushings must occa- 

 sionally have occurred, giving rise to fusion of rocks and limited 

 fissure-eruptions, or at least to pasty rock intrusions — as sug- 

 gested by Dana for granitic and analogous veins, that show no 

 evidences of the cooperation of very high temperature in the 

 act of formation. 



LeConte's view, that the first mashing of a geosynclinal 

 would produce less heat than later plications*, in which (pre- 

 sumably) a greater resistance would have to be overcome, seems 

 hardly to be compatible with facts as generally observed away 

 from the Pacific-coast eruptions; and his argument is the less 

 cogent, as the temperature produced is a function, not only of 

 the resistance of the rocks, but also of the degree and rapidity 

 of the motions, both of which have been on the decrease in late 

 geological periods, in accordance with the diminishing rate of 

 contraction of the earth and the increased resistance of the crust 

 to flexure. 



While Mallet's theory accounts satisfactorily for earthquake 

 phenomena and volcanic activity as manifested since the cessa- 

 tion of fissure-eruptions, and also for the gradual or sudden 

 depression of both large and small areas even subsequent to 

 that time, it makes no provision for their elevation, and there- 

 fore leaves unexplained the numerous oscillations of level of 

 which we find the record down to our own time. In assuming* 



* " On the great Lava-flood of the West/' Silliman's American Journal, 

 March 1874, p. 179. 



