368 W. A. E. TTSSHEK ON THE TRIASSIC 



The variegated marls outcropping, from beneath the Liassic 

 strata in the east occupy the lowest tracts of land covered by 

 the secondary rocks, capped here and there by Liassic beds, where 

 hills of sufficient height to allow of their presence occur, or 

 where exceptional cases of fault have rendered both equally sus- 

 ceptible to the forces of denudation. The scanty herbage some- 

 times permits the junction between the marls and overlying 

 Rhastic beds to be seen, even at a considerable distance, on the 

 slopes of these outliers, the grey and cream-coloured marls of the 

 Rhastic offering a marked contrast to the green-, grey-, and red- 

 banded marls of the Trias. 



As a general rule, greenish and bluish grey tints are most pre- 

 valent in the upper portions of the marls. Bands of greenish grey 

 calcareous stone are frequently met with, sometimes occurring in 

 laminae, upon the surfaces of which pseudomorphs of crystals of 

 rock salt have been occasionally discovered. Mr. Bristow found a 

 specimen in the railway-cutting between Shepton Mallet and Wells 

 during my no\iciate in field-work. Bluish mottling and banding 

 is not uncommon in the marl. 



Sandstones appear to be intercalated with it, but in very excep- 

 tional cases, where we were unable to ascertain their thickness or 

 relations to the underlying beds. 



At Claverham, near Yatton, grey sandstones occur which are 

 much used in the neighbourhood for building-purposes, owing 

 to their durability and hardening on exposure. The local epithet 

 for these beds is Clar'ham stone ; but whether they occur as a small 

 lenticular patch in the marl, or as a boss of a subjacent extensive 

 bed, there only brought to the surface, we are unable positively to 

 say, though from the proximity of Carboniferous sandstones capable 

 of furnishing them, and the fact that similar beds have not been 

 traced, wc arc inclined to the former hypothesis. 



At Ridge Hill, on the west of Chew Stoke, beds of soft sandstone 

 are shown under the marls in a road-cutting. Here again the 

 proximity of a patch of Millstone Grit at Leigh Down, about half a 

 mile to the northward, is sufficient to explain their presence ; but 

 their vicinity to the conglomerates on the north, and the occasional 

 presence of arenaceous beds at the base of the marls, render it 

 difficult to determine whether they do or do not rest on the con- 

 glomerates directly, their junction with them being concealed by an 

 overlap of marl. 



Arenaceous beds outcrop at the base of the marls, near Backwell, 

 between Brockley Elm and Yatton, between Yatton and Wrington, 

 and also at Churchill ; they are best developed near Roddy to the 

 north of Congresbury, and at Churchill. 



The irregular junction sometimes noticeable between the marls 

 and conglomerates, and the very unequal breadth of outcrop 

 exhibited within short distances by the latter, render it probable 

 that these sandstones may represent portions of arenaceous deposits 

 thrown down further from the old Triassic shores, and subsequently 

 overlapped by muddy sediments, as a progressive subsidence nar- 

 rowed the limits of the existing land, 



