200 



APPENDIX. 



this is evidently not correct. Mr. Hall explains the plication of the strata as the result of tha 

 svnclinal subsidence of the whole area, causing a crumpling of the beds in the upper portion of 

 the mass. Such a mode of production would necessarily entail a line of maximum depression 

 within the area of subsidence, and from which the plications would taks their origin in a 

 manner approximately symmetrical on either side. The facts, as given by Mr Kogers, seem 

 quite independent of any such area of subsidence. 



In the theory we have last considered, and, indeed, in every discussion involving depression 

 or subsidence of strata, there is a very important element which is commonly lost sight of, 

 namely, the earth's curvature. We are very naturally accustomed to look upon the bottoms 

 of seas, and, in general, any area of deposition as hollows, or actual concavities of the surface. 

 Mr. Hall, for instance, speaks of the lower strata of the Appalachian area during depression as 

 subjected to tension, resulting in fissures, and the consequent intrusion of igneous rock. A moi'e 

 correct representation of the conditions would have greatly strengthened the main conclusion for 

 which he argues. In point of fact, the depression would have probably involved the corrugation 

 of the whole thickness of the deposit and thereby magnified the bulging by which he considers 

 the chain to have been produced. The following table, taken from De Beaumont's work 

 already quoted (p. 1260), exemplifies this fact :— 



Distance 

 (arc). 



Maximum 

 depth. 



Height of sur- 

 face above 

 chord. 



Height of bed 

 above chord. 



The Channel, from Dieppe to Hastings 



Lake Superior, from Kurewaye Point ) 

 to Michipicoton j 



Caspian Sea, from Nizabad to Coast 

 of Asia 



Baltic, from Memel to Oland 



North Sea, from Whitby to Jutland ... 



Mediterranean, from Toulon to Phi- ) 

 lippeville J 



Kilom. 

 Ill 



159 



246 



290 



600 



733 



Met. 

 59 



241 



200 



100 



100 



2600 



Met. 

 242 



503 



1123 



1651" 



6900 



10534 



Met. 

 183 



259 



923 



1551 

 6800 



7934 



From this it appears that the Mediterranean, supposing for illustration's sake, that the 

 deepest point is about the centre, might be filled up with a deposit to a depth of 7,000 



