BucMand^s Formation of the Valley of Kmgsclere. 269 



deluge; and, in so doing, they would only conform to the 

 course of all the other formations which crop out to the west- 

 ward of them. 



The tender and destructible nature of the deposits above 

 the chalk, would render them peculiarly liable to be swept 

 away, in some parts, by diluvial currents. Their preservation 

 at other points, and " their separation into the two distinct 

 basins of London and Hampshire, have resulted partly from 

 local elevations and depressions, by subterraneous violence, 

 since the deposition of the plastic clay, and partly from the 

 still more recent removal of much of their substance by diluvial 

 denudation." (Geol, Trans., vol. ii. p. 127.) 



Before concluding this article we must return to Mr. Mar- 

 tin, on the supposed depositions of strata in basins. " Although 

 the contents of these chalk basins have been carefully ex- 

 amined and described, no satisfactory explanation of the 

 mechanism or mode of formation of the basins themselves has 

 yet been given ; and, since the French naturalists first made 

 use of the term, so much laxity has obtained in the application 

 of the word basin, that it is made to comprehend almost every 

 depression in the earth's surface." {Martin, p. 55.) 



" The obscurity in which this branch of the subject has 

 been left, appears to have arisen from the difficulty of con- 

 sidering it apart from a general theory of displacement, and 

 from the conflicting opinions prevalent upon that subject ; and 

 because geologists, not professed Vulcanists, have been in the 

 habit of considering all displacement as the effect of one of 

 two causes — of subsidence from simple gravity, or excavation 

 by watery erosion." {Id., p. 56.) 



" But, in whatever mode these basins exist, they have been 

 considered as the recipients and continent cavities of succes- 

 sional deposits of different eras and different agencies ; and 

 their preexistence is necessarily involved in that consideration. 

 How far this theory agrees with appearances developed by 

 later discoveries, remains to be proved. Some relaxation of 

 the original idea of deposits in the Paris basin exclusively is 

 said to have been made ; and the discovery of the same strata 

 elsewhere in a horizontal, and what may be considered an 

 original position, serves to strengthen the opinion, that the 

 strata above the chalk are all of a date anterior to the con- 

 vulsion which divested it of its flotz character." {Id., p. 57.) 



In another place he observes, " Of the English basins it 

 may be safely asserted, that, being fissured in all their parts 

 in the act of subsidence, and many parts of them of higher 

 level than the intervening excavations, no deposit co?dd have 

 taken place "within them which did not fill denuded cavities. 



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