28 



I he BRISTOL I OALFIELD. 



Carboniferous art icks generally, the particles of silica cement 



themselves together, possiblj by the cohesion of the particles assisted 

 ■ urn il pressure. 



i i it is due to the rock having been 



or millstone . but it is also known in other parts of England as 

 the- •• Farewell" rock, as being the base of the coal measures. When it is 

 met with the miners know that they have come to the end of produc- 

 tive ooal-bearing Btra 



Now, arisen in determining this rock, others 



higher op in the aeries of coal-bearing strata, having been mistaken for 

 ,;. For i I ■'■ . the " Black Vein" grit of the middle series is, so 

 far as ohemical composition and lithological features are concerned, a 

 Millstone grit, putting aside, of course, the question of thickness. 

 This will be Bhown bj the following analysis : — 



ANALYSIS OF THE BLACK M.1N STONE. 



lica 97-33 



Alumina 9G 



Iron -50 



Lime "40 



sous Matter '-45 



Carbonic Aoid "60 



Water -15 



100'39 



development ofgrit above tin- Millstone gritin the Lower 

 ires is locally known as the " Hard Venture." 

 > : i cal stone, I apart, gave the following 



analysis : — 



ANALYSIS ,iF Hit "HARD VENTURE" OIUT. 



Silica 



Alumina 



Iron 



Lime 



ii 







No. 1. 



No. ■>. 



100-16 



10053 



DETAILED ANALYSIS. 



ee which can be relied upon is, that the Millstone grit has 



