APPENDIX. 197 



secondary effect, awl one would expect to find in the region east of the Appalachians, sup- 

 posing the section visible, a system of disturbance equivalent to that on the west. The only 

 other alternative seems to me to involve a great modification of Mr. Rogers' theory of elevation, 

 and to imply a far greater influence of superficial, modifying causes than he makes any 

 allowance for. Accepting the features of contortion described by him we must still believe the 

 centre of disturbance to be external to the present chain, but we can greatly modify the 

 nature of that disturbance ; we can eliminate the idea of great central upheaval and suppose 

 that zone to have been one of weakness and of fracture, and hence a locus of disturbance. 

 The very great difference of conditions which we can reasonably suppose to have obtained on 

 different sides of this central line of intensity removes the necessity for similar effects of 

 disturbance on these two sides. In this way we are led to reject the supposition of sj'mmetry 

 being the necessary type within regions of disturbance, so distinctly implied in Mr. Rogers' 

 statement of his theory. Mr. Rogers makes no allusion to the difficulty I have just attempted 

 to explain as involved in his theoiy, but by the facts adduced in the descriptive part of his 

 work he leaves little doubt as to the relation of the Appalachian rocks to those of the region 

 to the south-east. We are led to believe that those gneissic rocks were in about their present 

 position from the earliest ages. From the first of the Primal strata to the topmost bed 

 of the coal-bearing group the area of deposition of the great Palaeozoic series is represented 

 to have been restricted pretty much as we now find it : and much of the material of these 

 deposits is represented to be derived from gneissic rocks in the approximate position of those 

 now existing. 



The grand result of Mr. Rogers' labours, the suggestion of a systematic arrangement in the 

 contortions of strata, as a statement of observation, remains unaffected by the modifications 

 we are compelled to put upon his theory. If his views prove to be generally applicable, they 

 will be of incalculable service in the interpretation of geological sections. 



Neither Mr. Hopkins nor Mr. Rogers offers any conjectures upon the prime cause of the 

 expansive forces to which they appeal as agents of distm-bance. 

 eoheii.' a ° " The omission of such speculations cannot be said to detract from 



the value of their researches ; the independent analysis of facts is 

 the first and the safest method of discovery, yet, as the knowledge of natural causes is the 

 ultimate aim of scientific investigation, our interest in a theory must be influenced by the 

 light it can throw upon these prime sources of activity. This is the secret of the fascination 

 we find in M. de Beaumont's work. For the same reason there is even a greater fascination in 

 a theory which I have now to notice. It is that proposed both by Mr. Babbage and Sir J. 

 Herschell from a priori considerations of the general condition of the earth, and it was 

 suggested to these philosophers by the want of a prime mover in the explanations 

 usually given of the phenomena of disturbance. We know from observation that the 

 temperature of the ground is distributed with reference to the form of the surface, and 

 that underground isothermal surfaces correspond locally in contour with that of 

 the external surface. The laws of conduction and radiation of heat show us that it 

 must be so. If therefore the form of the surface were to be altered, if any elevated 

 mass of land were to be lowered, or if any depression were to be filled up, the law 

 just stated would after a time prevail over the area thus altered. If we consider the 

 consequences entailed by this change it will be seen what great results may be produced. 



