﻿Vol. 66.~] JURASSIC STRATA OF SOUTH DORSET. 57 



II. Description of the Strata. 

 (a) Chideock. 



There is a very interesting and fairly continuous section from 

 the top of Chideock Quarry Hill to the cliffs by the seaside. The 

 sequence on the hill is difficult to follow, because there are only 

 shallow workings and most of these are closed ; so, in my former 

 paper, the extent of the beds on the Chideock Quarry Hill was 

 understated, owing to the difficulty of seeing junctions properly. 1 

 The same cause may affect the section now tabulated ; but more 

 details have been obtained, and the method of dating the beds is 

 more exact and elaborate than was in use at that time. 



In the same paper was given a section of part of Down Cliffs — 

 the cliffs to the south of Chideock on the sea-coast. Here there was 

 an omission. It was noted in the paper (p. 519) that there was no 

 evidence of the dispansum, striatuhim, and variabilis beds, and it 

 was stated that they ought to come in at the base of the Blue Clay, 

 there numbered Bed 9, or at the top of the Junction Bed, there 

 numbered Bed 10. Subsequent discovery verified that surmise ; for, 

 in certain places, at the top of the Junction Bed there is a thin layer 

 (2 inches) of a light-coloured stone containing ammonites of the 

 Grammoceras-striatidum 2 series. But in many places, even where 

 the Junction Bed is investigated in situ in the cliffs, this layer is 

 absent. However, it has also been found in the fields on the west 

 side of Chideock Quarry Hill. Then, in a road-cutting at Symonds- 

 bury, there was found further evidence of deposit of this date — a 

 specimen of Haugia fascigera encrusted with irony matter. 



At about the same time that I had noted the occurrence of 

 Grammoceras-striatidum forms near Chideock, the late Mr. J. F. 

 Walker had made the same discovery near Bridport, where he quotes 



* Am. (Harpoceras) striaiulum' and ' Am. ( Grammoceras) thou- 

 arcense \ 3 He had, however, announced a further discovery — that 

 of Ammonites germa[i]ni, d'Orbigny, in a higher layer. 4 With his 

 usual kindness he gave me examples ; and, though I have not seen 

 the rocks in situ myself, I consider that Am. germaini indicates 

 the presence of some portion of the dispansum zone : at any rate, a 

 layer lower than the Blue Clay of Down Cliffs. This layer has not 

 been found in the coast-sections. 



The top bed of Chideock Quarry Hill consists of several feet of 

 blue clay of the Fullers' Earth. Below this are some 14 feet of lime- 

 stones — actual limestones which can be burnt for lime. No evidence 

 was found of the upper or zigzag layer, and nothing was seen of 

 any evidence for the lower or truellii layer ; hence it is presumed 

 that all these limestones belong to the intervening layer which may 



1 ' On the so-called " Upper Lias " Clay of Down Cliffs ' Quart. Journ. Geol. 

 Soc. vol. xlvi (1890) p. 519. 



2 To find the author's name, etc., of Ammonites thus mentioned, consult Index , 



* Monogr. Inf. Ool. Amm.' (Palseont. Soc.) 1907. 



3 Geol. Mag. dec. 3, vol. ix (1892) pp. 440, 442. 



4 Ibid. p. 442. 



