78 Notices of Memoirs — E. Wethered — Clifton Rochs. 



between the curves are partially eroded and filled with irregular 

 detrital material containing oolitic grains. 



The surface of the block presents an irregular concretionary 

 structure, resembling that seen on many varieties of Gotham Marble ; 

 but it is not so pronounced as in some of the mammillated surfaces 

 seen in that rock. 



The appearances are probably due to mechanical disarrangement of 

 the upper layers produced prior to and during the consolidation of 

 the rock, and they suggest a pause in the deposition of sediment. 



It is noteworthy that the darker bands which produce the 

 arborescent markings stand out slightly in relief on the weathered 

 face of the block of Carboniferous Limestone. This is also the case 

 ■with an example of Cotliam Marble which I lately obtained on the 

 South Wales Direct Railway at Stoke GifFord. 



A small specimen of Carboniferous Limestone from Backwell, 

 near Nailsea, given to me by Mr. W. H. Wickes, shows indications 

 of arborescent markings. [Further references to the subject are 

 given in the Geol. Mag., Dec. Ill, Vol. IX, 1892, p. 110, and in 

 " The Jurassic Rocks of Britain," Mem. Geol. Surv., vol. v, p. 230 ; 

 see also B. Thompson, Quart. Journ. Geol. Soc, vol. l (1894), p. 393.] 



YI. — The Building of Clifton Eocks. By E. Wethered, F.G.S.^ 



IN this paper the author confines his remarks chiefly to the 

 microscopic life which he has discovered in the Carboniferous 

 Limestone rocks at Clifton. He contends that microscopic calcareous 

 organisms have been the chief contributors to the vast deposits in the 

 Carboniferous sea, now represented by the cliffs on either side of the 

 gorge of the Avon at Clifton. 



Broadly speaking, there were three stages in the formation of 

 this limestone. These were regulated by physical conditions, and 

 favoured the existence of certain forms of life. The fossil remains 

 now denote the stages. They are as follows : — 



Approximate Thickness. 

 Stage 1. Lower Limestones (inchiding the Lower 

 Limestone shales, 500 feet, and Black Eock 



series, 470 feet) 990 feet. 



Stage 2. Middle Limestone 1,620 „ 



Stage 3. Upper Limestone 100 ,, 



The close of the Old Eed Sandstone period is marked by variegated 

 sandstones and shales. These beds pass into limestones and shales, 

 and these again are followed by massive limestones locally known 

 as the Black Eock ; the whole representing the Lower Limestones, 

 or Stage 1. 



During this stage encrinites were so numerous in the waters that 

 the ossicles of these creatures are a distinguishing feature of the 

 limestones. Vast numbers of ostracoda at times lived, and some 

 beds of the limestone are chiefly accumulations of the remains of 

 these small crustaceans. Monticulipora corals and polyzoa were 

 numerous in the waters, and also mollusca. 



1 Eead before Sect. C (Geology), British Association, Bristol Meeting, Sept. 1898. 



