, 458 



with it at a few isolated points, viz. , at Tyning's, near Codrington, 

 at Doynton, Wick and Beech, but these are valuable landmarks in 

 determining the eastern limit of the basin. 



Outcrops of Millstone Grit. 



The Millstone grit is a deposit of much less importance than that 

 I have been describing, and as it lies nearer the base of the hills, it 

 is much covered up by secondary rocks. The only connected out- 

 crop of it on the south side of the basin is between Mells and 

 Ashwick, where it occupies a considerable area, but it is seen at one 

 or two isolated points besides. At Emborrow, where I examined 

 the ground in company with a friend in the course of the present 

 autumn, we detected to the north and east of Lechmere water 

 what we believed to be unmistakeable outcrops of the rock. These 

 are not shewn in the Ordnance Map, which at this point does not 

 exhibit the usual amount of accuracy, portions of the grit and of 

 the true Coal measures having been coloured as mountain limestone. 

 Mr. Saunders also appears to have discovered outcrops of the grit 

 at Compton Martin and Winford which had escaped the notice of 

 the Government Geologists. 



Passing northward it appears in a succession of patches extending 

 from Long Ashton to Durdham Down, and we then see no more of 

 it until we reach Tytherington, from whence it passes round the 

 northern end of the basin by Cromhall to Yate. At Cromhall it 

 belies its usual character of being the miner's farewell rock, for 

 workable seams of coal have actually been found in it. ^\iter leaving 

 Yate the only point at which it is exposed is Wick, where it flanks 

 the limestone on two sides. 



Outcrops of Coal Measures. 



Taking then the outcrops of the Old red sandstone in connexion 

 with the ranges of Mountain limestone and Millstone grit by 

 which they are flanked, we get a general outline of the basin of 

 productive Coal measures lying to the north of the Mendip Hills. 

 Within this basin as I have already stated there are few outcrops 

 to guide us, and from the prevalence of shales which are much de- 

 composed near the surface, coal measure outcrops are generally less 

 instructive than most other rocks. 



