Mr. Lonsdale on the Oolitic District of Bath. 



243 



The range of the chalk hills rises either suddenly from the gault^ as be- 

 tween Westbury and Earl's StokC;, and Roundaway Hill and Cherhill; or 

 from a terrace of the upper greensand^ as between Earl's Stoke and Devizes. 

 The hills present the usual rounded outline, but are not cut through by any 

 transverse water-courses. The vale of Pewsey, at its entrance, is about 300 

 feet above the level of the second plain, and its streams flow to the south-east 

 in the direction of Amesbury and Salisbury. The escarpment of the range is 

 composed of the upper greensand, the chalk marl, and the lower chalk. 



I now proceed to describe the nature of each formation. 



Lias . 



In treating of the Lias, I purpose to consider it under two heads, the Lias 

 of Bath, and that of Radstock, as some interesting peculiarities distinguish the 

 formation at the latter locality. 



The accompanying Table presents a general type of the lias in the neigh- 

 bourhood of Bath. 



Descriptions. 

 1. Lias Upper Marl. .Blue clay and marl; which are" 

 tough in the lower part of the 

 deposit, but thinly laminated 

 ai 



ii\d micaceous in the upper. Ir. f 

 egular beds of stone are inter. | 



Thickness. Localities. 



f Walcot : Batheaston : 



200 feet. -^ Beechen Cliff: the 



L upper part of Bath. 



stratified with them J 



2. Blue Lias Beds of greyish, argillaceous lime-") 



stone, varying in thickness from 



2 to 1 8 inches, and separated by I ^Q ^^ gQ j.^^,^f W 



others ot blue marl which are I i i 



generally less than 6 inches thick, j 



but sometimes more than 2 feet. J 



eston : Upper Bris- 

 tol Road: Twerton. 



3. White Lias Thin strata of yellowish white, ar.") 



gillaceous limestone, with part- i>10 feet 

 ings of pale brownish clay 



4. Lias Lower Marl. .Dark grey marl with calcareous 



concretions 



r 



i 



rWick. This division is 

 I seldom exposed in 



the immediate vici- 

 L nity of Bath. 



^ 20 feet Very rarely exposed. 



Of these divisions, the 1st and 4th require no further explanation; but as 

 an account of the beds comprising the 2nd and 3rd has not yet been published, 

 the following enumeration is given from a quarry situated on the southern 

 side of the Bristol Upper Road, and about one mile and a half from Bath. 



Top. 

 Three beds of greyish limestone se- 

 parated by layers of friable, gritty 

 marl 



" Fire clay," mottled, gritty marl . . . 

 *' White bed," greyish limestone. . . . 



Blue Lias. 



Ft. In. 



Ft. In. 

 Friable, gritty marl, inclosing nodules 



of indurated marl 6 



" Oaty bed," grey limestone 10 



Friable, gritty marl 2 



" Double bed," grey limestone 1 



I ^4 



