tin; kh.ktic kocks at i'YLLk hill. ^54.1 



30. Oil a Section of the Kh.'ktic Rocks at Pylle Hill (Tottekdown), 

 Bristol. By Edw. Wilson, Esq., F.G.S., Curator of the 

 Bristol Museum. (Head May 0, 18i)l.) 



Although the Rhaetic rocks have a wide horizontal distribution iu 

 the iiei<^hbourhood of Bristol, it is but seldom that they are exposed 

 at the surface, iu the abseuee of natural inland sections, nnd of 

 quarries on the horizon of a thin series of rocks which yield no 

 minerals of commercial value, we have generally to trust to new 

 railway-cuttings or other artificial excavations for affording us 

 opportunities for their examination. The construction of the 

 Bristol Relief Railway has, in this way, recently given us an ex- 

 cellent section of these rocks. 



In the deep cutting of this railway at Pylle Hill, Totterdown, on 

 the south side of the city of Bristol, we get the following interesting 

 rock-sequence. From the level of the line to a height of about 

 forty feet above it, the red and green marls of the Upper Keuper 

 are exposed. These variegated marls terminate upwards in nine 

 feet of light greenish-grey marls — the " Tea-green Marls " of 

 Etheridge. Above the Keuper Marls come the Rhaetic Beds, com- 

 prising two well-marked subdivisions, namely the black " paper 

 shales " of the Avicula-contorta series below, and the light grey 

 limestones and laminated shales of the Upper Rhaetic series above,, 

 the two series taken together being only seventeen feet in thickness. 

 The Rhaetic Beds are succeeded by three or four feet of rubbly, 

 cream-coloured limestones and shales, usually termed " White Lias," 

 and the section is completed by some nine or ten feet of the regu- 

 larly bedded limestones and shales of the Lower Lias, containing 

 fossils characteristic of the zone of Ammonites planorhis. 



The railway runs E. and W., or approximately along the strike 

 of the beds — the dip being S.S.E., at an av^erage angle of from 3'^ 

 to 4°. In the line of section the beds are nearly horizontal, but 

 with a very gentle synclinal arrangement *. 



This is not the first time the Pylle Hill section has been described. 

 In the year I860 the late Charles Moore read a paper before this 

 Society "On the so-called Wealden beds at Linksfield, and the 

 Reptiliferous Sandstones of Elgin," an abstract of which, published 

 in the Quarterly Journal for that year f, gives a section at " Pylle 

 Hill on the Bristol and Exeter Railway," and therefore at a very 

 short distance from the section now under consideration. 



The section given by Moore is, however, so incomplete, and the 



* Owing to the form of the ground — the railway cutting through a hillside 

 with a steep slope to the iiortli — and to the southerly dip of the beds, the Lower 

 liias and Upper Eha.^tic' beds here referred to are shown in the southern, but 

 not in the northern side of the cutting, and the horizontal section, which is 

 taken along the centre line of the railway, also shows considerably less of the 

 upper beds than the vertical section, which is constructed from measurements 

 made on the south side. 



t Quart. Journ. Geol. Soc. vol. xvi. p. 446. 



