APPENDIX. 199 



the region of the Alleghanies, amounting to no less than 40,000 feet, while in the 

 country to the west, where the same series is comparatively undisturbed, the total thick- 

 ness is not more than 4,000 feet. He gives reasons for supposing that this enormous 

 accumulation of deposits was mainly derived from sources which lay to the eastward and 

 northward. The region of greatest deposition has been also that of chief disturbance. This 

 last fact, which may be only a coincidence, is accepted by Mr. Hall, without discussion, as 

 affording a final explanation ; he says, " The line of the greatest accumulation is the line of the 

 mountain chain ; in other words, the great Appalachian barrier is due to original deposition 

 of materials and not to any siibsequent action or influence, breaking up and dislocating the 

 strata of which it is composed." The existence of ripplemark, of marine plants, &c, shows 

 that the deposition throughout the series took place in moderate depth ; continuance of 

 accumulation produced continued subsidence ; this prolonged subsidence resulted in the 

 production of a great synclinal depression which is still a feature of the Appalachian 

 structure. During depression the bottom strata suffered distension and fracture, and the 

 upper underwent compression and folding. Mr. Hall attributes the entire elevation of the 

 Appalachian range to this indirect agency, namely, the bulging of the upper crust produced 

 by the plication during general subsidence. In this he seems somewhat inconsistent with 

 the general theory he adopts— that of Babbage and Herschell. He seems to admit no direct 

 local elevation of the rocks composing the Appalachian chain. But such local elevations 

 form a prominent and a necessary feature of the general theory, and an ultimate rising 

 by the general increase of temperature of the earth's crust beneath an area of deposition 

 is as certain, or more so, than is the prior depression of that area, owing to continued 

 accumulation of rock-matter. Mr. Hall appeals vaguely to continental elevation without 

 any allusion to the cause of a phenomenon so opposed to the general tenor of his 

 views. In alluding to the great allied question of metamorphism he is equally vague 

 and inconsistent. He says, — " We must therefore look to some other agency than heat 

 for the production of the phenomena witnessed, and it seems that the prime cause must 

 have existed within the material itself, and that the entire change is due to motion, or 

 fermentation and pressure aided by a moderate increase of temperature, producing chemical 

 change." In extending his views of superficial agencies, Mr. Hall states it as his opinion that 

 overflows of trappean matter are always coincident with the rapid accumulation of sedimentary 

 materials. Without special allusion to the structure of other mountain areas, Mr. Hall 

 asserts the universality of these principles of formation for all mountains, and he attempts to 

 establish a relation, founded on this principle, between the height of a chain and the range of 

 geological formations, involved in its production, and exhibited in its structure. For example, 

 he says, " if the fundamental rocks of the Alps are of palajozoic age, and the sequence has been 

 continued, even with some interruptions, to the end of the Jurassic period or later, it is no 

 wonder that there are high summits, for the accumxdation must have been enormous, and if to 

 the Liassic and Jurassic we add the Cretaceous and Tertiary, we may get mountains of the 

 elevation of the Himalaya." 



Regarding that most interesting question of the form of the plications of the strata in the 

 Alleghanies, Mr. Hall leaves us in great doubt. He gives no sections in the work from which 

 I quote, but he seems to adopt the facts as stated by Mr. Rogers, simply asserting that his 

 theory of subsidence gives a sufficient explanation of those facts. As I understand the case, 



