270 Mr. Lonsdale on the Oolitic District of Bath. 



and Westbury Leigh to Isomley. At this village begins a projecting ridge 

 of upper green -sand, which reaches by Chapmanslade to Berkley Lodge. 



Chalk Marl. 



The chalk marl presents no peculiar characters. Its general appearance is 

 that of a grevish white, argillaceous, soft limestone, the detached blocks of 

 which on exposure to the weather descpiamate into small globular or sphe- 

 roidal masses. Near Warminster some of the beds contain much fine sand 

 disseminated through the cretaceous basis. Streaks of grey or pale blue fre- 

 quently traverse the strata, and become on being wetted almost black. The 

 passage from the upper green-sand into the chalk marl is often well displayed, 

 and is generally effected in a very few feet. 



The chalk marl ranges along the centre of the escarpment of the hills bor- 

 dering on the Marlborough Downs and Salisbury Plain. At the gorge of the 

 vale of Pewsey it has been almost entirely removed by denudation, only two 

 small eminences being left, the highest of which is called Etchilhampton Hill. 



Lower Chalk. 

 The lower chalk, which forms the summit of the downs in this part of Wilt- 

 shire, consists of beds of soft chalk alternating with others composed of 

 roundish nodules, and with strata of a hard, splintery limestone, which yields 

 to the frost. The accompanying section from Bratton Castle near Westbury 

 will illustrate the connection of these varieties of stone. 



Top. Ft. In. 



Malm, or rather soft chalk 1 6 



A layer of flints. 



Roundish nodules of hard chalk, of a ferruginous colour 9 



Hard, splintery, white limestone 1 



Malm 2 6 



Roundish nodules of hard chalk of a ferruginous colour 1 2 



Hard, splintery, white limestone 1 6 



Malm. 



At Cherhill, well known to the traveller by its White Horse, the hard, 

 splintery, limestone is wanting, and the formation is composed of alternations 

 of malm and round nodules ; but the former greatly preponderates in quantity. 



Gravel. 



Extensive beds of gravel accompany the Avon through the whole of its 

 course from Kelloway to Keynsham, but they do not present any peculiar 

 features, and are formed of the debris of the neighbouring rocks. !n the 

 vicinity of Farleigh are likewise widely spread accumulations, composed of 



