228 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 8, 



2. Some Remarks on the Denudation of the Oolites of the Bath 

 District, with a Theory on the Denudation of Oolites generally. 

 By W. Stephen Mitchell, Esq., M.A., LL.B., E.G.S., of Gonville 

 and Caius College, Cambridge. 



[Abridged.] 



The theory commonly held as to the origin of the Oolite hills of 

 this country is, that the strata of which they are composed were 

 originally deposited in sheets continuous over large areas, that the 

 valleys are entirely the result of denudation, which has left the 

 intervening masses standing out as hills, and that it is generally 

 possible to recognize on opposite sides of a valley at the different 

 horizons the individual beds which were formerly continuous across 

 that valley. The author believed that the following theory had 

 equal claims to credence : — 



That the sedimentary deposits of any particular Oolitic district were 

 prohahly originally deposited in continuous heels, hut that the lime- 

 stones in many instances prohahly never extended heyond the areas 

 they now occupy. 



The object of the paper was to show that the Bath district was 

 one of these instances; and the following were the chief points 

 brought under the notice of the Society. 



In the Bath district, whUe the beds of the Great Oolite lime- 

 stone are for the most part approximately horizontal over the pla- 

 teaux of the downs, they thin out at the edges of the hills. Mr. 

 Sanders in his map of the district has marked the few Oolite hills 

 which come within the map as everywhere dipping towards the 

 valleys. 



There is no evidence here of a washing away of the underlying 

 Fuller's Earth, and a consequent drop of the limestone, as is sug- 

 gested by Mr. Witchell to be the case in the Cotteswolds*. The 

 Euller's Earth might be scooped away for many feet under the 

 limestone before the latter would move. "When it did move, it would 

 probably break off and slip or roll down the hill-slope. Here the 

 thinning out is the same when other beds of the limestone underlie ; 

 there is no displacement from the general mass. [It is just possible 

 that they may be cases of false bedding, with the layers that were 

 above them swept away ; but the author could not see by what 

 agency this would be effected.] 



To explaiu this thinning out, the probable origin of the beds was 

 taken into consideration. 



I. The limestones. — The commonly received view that the material 

 of the Great and of the Inferior Oolite was accumulated by corals 

 was supported by quotations from Jukes's ' Voyage of the Ely,' and 

 Darwin's ' Voyage of the Beagle.' Becent coral-reefs are described 

 as consisting of " rock fine-grained, only here and there exhibiting 

 any organic structure." They show lamination and a jointed struc- 

 ture; and the bedding round the edges of an island dips towards the sea. 



* Proceedings of the Cotteswold Nat. Club, 1867. 



