﻿part 1] igneous rocks or the Bristol district. 25 



No allusion to these rocks is made in the Geological Survey 

 Memoir on the East Somerset & Bristol Coalfield, published in 

 1876 ; but two patches are shown as intrusive masses in the 1-inch 

 Geological Survey map revised to 1873. In the account by 

 Sir Archibald Geikie and Dr. Strahan of the volcanic group in the 

 Carboniferous Rock s_ of North Somerset 1 it is suggested that the 

 two outcrops may belong to the same band, and it is mentioned 

 that the western one was traced for some distance by means of 

 debris thrown out by moles. In the 1-inch Geological Survey 

 map, with additions to 1899, which is at present on sale, the out- 

 crop of the igneous rock is shown as forming an oval ring. 



Western group of exposures. — These lie in the neigh- 

 bourhood of the footpath which, diverging from the main path 

 due south of Warren House, trends in a north-easterly direction. 

 It is clear, from the material thrown out by rabbits, that lava 

 occupies a considerable area in this neighbourhood, and the digging 

 of a series of trial-holes showed that the exposure is shaped some- 

 what like a boomerang — one arm extending a considerable distance 

 up the hillside south-south-east of Warren House, while the other 

 crosses the main path and runs up the slope to the south. 



I am confident that the ring-shaped outcrop as marked in the 

 latest 1-inch Geological Survey map does not accurately repre- 

 sent the facts, and that for a long distance along the northern 

 line of the supposed outcrop, and for a shorter distance along the 

 southern, the rock really present is limestone. Along the line of a 

 track (not shown in the 6-inch map) which leads off to the left 

 from the north-eastward-trending path alluded to above, occurs 

 •a relatively continuous section of calcareous tuff which was 

 further exposed by pick-work. The rocks dip at about 15° in a 

 westerly direction, and clearly overlie the lava. The section is as 

 follows : — 



Thickness in feet. 



6. Red sandy limestone passing up into pale calcareous sandstone, 



and down into moderately coarse calcareous tuff about 22 



5. Fine green calcareous tuff about 9 



Gap of about 5 feet. 



4. Fine greenish calcareous tuff very poorly exposed about 5 



Gap of 30 feet — nothing seen, except a small and poor exposure 

 of dolomitized limestone. 

 3. Red and greenish calcareous tuff, sometimes gritty, sometimes 



rather coarse, exposed by pick- work say 8 



Gap of 8 feet. 

 2. Band of Carboniferous Limestone. 



1. Basalt (81) exposed by trenching at the bottom of the lateral 

 valley. 



The limestone (band 2) is probably on the strike of a mass 

 exposed in the angle between the main path through the Combe 

 and that which diverges to the north-north-east. 



1 ' Summary of Progress of the Geological Survey for 1898 ' Mem. Geol. 

 Surv. 1899, p. 110. 



