CHALK. 83 



Gault in Compton Bay. A poor representative of the Melbourn 

 Kock was detected here by Mr, Whitaker, the sequence being 

 as below : — 



rMassive thick-bedded chalk traversed by straight 



Mid.ile Chalk^ Melbourn Rock, hard thinly bedded chalk with layers 



L of marl, about 8-10 feet. 

 Lower Chalk - Softer chalk, traversed by curving joints, producing 

 ' conchoidal fracture ' on a large scale. 



A small fault throws the beds about 6 feet down to the north- 

 west, at the point where the Melbourn Rock comes down to the 

 beach. Downwards the Lower Chalk passes so gradually into tlie 

 Chloride Marl that it is difficult to fix its base. The following 

 section, which forms the continuation of that given on p. 68, was 

 obtained by climbing a short distance up the cliff. 



Ft. In. 



Alternations of chalk and marl in beds of 1-2 feet thick. 



Chalky sand, with glauconite, and containing rolled Ammo- 

 nites, Turrilites, &c. at base. The bed looks like chalk 

 at first sight, but contains perhaps more sand than chalk - 8 



Pale-blue marl and chalk in alternations - - - 7 



Chloritic marl (see p. 81). 



Along all this part of the coast, from Compton Bay to Sun 

 Corner, a line of rocks may be seen under the water when the 

 sea is smooth and clear, running nearly parallel to the foot of 

 the cliff, and still more nearly parallel to the line marking the 

 top of the Middle Chalk, as traced above. This line of rocks 

 marks the submerged outcrop of the Chert Beds, for further east 

 it joins a reef formed by these beds, which is bare at low water 

 in Compton Bay. It shews no deviation from its course opposite 

 Freshwater Bay, whence we may infer that no fault runs alono- 

 this valley, where a fault might have been suspected from the 

 course taken by the topmost beds of the Chalk. 



Following the Downs eastwards, we find the next sections at 

 the south-eastern corner of Shalcombe Down. Here there are 

 two pits, the upper of which was described by Mr. Whitaker.* 

 The section seen in 1887 was as follows : — 



Pit at the south-eastern cornier of Shalcombe Down. 



Ft. In. 

 Chalk with flints ----_. 



Rough nodular chalk without flints - - - - 10 6 



Black clay or shale - - - - - -01-3 



Rough nodular chalk - - - . - 6 



Nodular bed (Chalk Rock), the nodules in the upper 3 inches 



green-coated - - - - . -13 



Massive thickly bedded chalk with two or three seams of 

 marl about 10 feet apart - - - . .20 0-f- 



The lower pit is in the lower beds of the Middle Chalk and 

 seems to touch the Lower Chalk, but the Melbourn Kock could 



* Quart. Journ. Geol. Soc, vol. xxi. p. 402. 1865. 



F 2 



