Geology of the Neighbourhood of Wei/mouth, ^c. 33 



is, the arch-like disposition of all the formations it contains ; the axis of this 

 arch passes east and west from Weymouth Bay to the Chesil Bank, forming 

 an anticlinal line, on each side of wliich all the successive strata dip respec- 

 tively to the north and south. This dip of the strata in opposite directions 

 from the anticlinal line, is represented in the general section, Plate II. fig. 1. 

 It affords, on a larger scale, an example of the same kind of valleys of eleva- 

 tion with those which have been described by Professor Buckland*. The 

 details of these arched strata in the Vale of Weymouth have already been 

 sufficiently set forth. We think there is evidence enough to show that the 

 strata were once nearly continuous and horizontal, and have been elevated 

 to their present position by a force acting from beneath in a line nearly east 

 and west, forming a continuation of the same line of elevation that extends 

 through Purbeck and the Isle of Wight, and parallel to that of the axis of 

 elevation of the Weald of Sussex and Kent. The period of elevation in all 

 these cases was apparently the same, viz. subsequent to the deposition of the 

 London clay, if not of the most recent tertiary strata in the Isle of Wight. 



With respect to the analogous axis of elevation, which extends with 

 certain interruptions from the eastern extremity of the Mendip Hills along 

 the coast of South Wales to Milford Haven, it has been shown by Dr. Buck- 

 land and Mr. Conybeare that this elevation took place before the deposition 

 of the new red sandstone formation f ; the direction of this line deviates from 

 east and west several points towards the north-west. 



In these comparatively small instances, as in the elevation of the highest 

 mountains in the world, noticed by M. Elie de BeaumontJ], it seems that 

 the operating forces have been exerted usually in straight lines, and that these 

 straight lines were often parallel to one another ; and the fact that the 

 greatest mountain chains are for the most part thus disposed, more especially 

 those which are volcanic, as in the case of the Andes, leads us to refer the 

 elevation of them all to one and the same common cause, — namely, the expan- 

 sion of elastic vapours bursting upwards in longitudinal cracks along the lines 

 where the least resistance was presented by the incumbent strata§. The 

 comparative insignificance of the elevations we are considering in the South 

 of England, makes no difference in the principles we would apply to explain 

 their origin ; they appear to us to be faithful models, representing on a smaller 



* Geol. Trans. Second Series, vol. ii. Part I. p. 119. f Ibid. vol. i. p. 210, et seq. 



X Annates des Sciences Naturelles, 1829 — 1830. 



§ The movement of modern earthquakes along straight lines, added to the frequent rectilinear 



position of volcanic chains, adds still further probability to these conjectures See Hall's South 



America. 



VOL IV. — SECOND SERIES. P 



