348 GEOLOGY OF THE BRISTOL COAL-FIELD. 



Professor MacLaren (Geol. of Pife, 116,) calculates that it would 

 require 1000 years to deposit sufficient material for a bed of Coal 

 one yard thick. Now our Bristol Coal-measures without the 

 Millstone Grit, have a thickness of 6725 feet of which only 100 

 feet are seams of Coal, the rest being sedimentary material which 

 Professor MacLaren calculates was deposited at the rate of two feet 

 per centnry. 



It would follow from this that the Coal would take (100 or 33^ 

 yards x 1000,) 33,333 years and 6725—100 = 6625 feet and 

 6625 X 100 + 33,333 = 364,583 years for the deposition of the 



2 

 whole Coal measures from the Millstone Grit upwards. 



Estimated Thickness of the Coalfield. 



MiUstone Grit - - - 1000 feet. 



Lower Coal measures- 2000 with 36 seams of Coal 72 feet thick. 



Pennant Grit - - - 1725 „ 5 „ ,. 10 ,, 



Upper Coal measure - 3000 „ 22 „ „ 18 „ 



7725 63 100 



The quantity of Coal waiting for extraction is very large, Mr. 

 Prestwich (Report Vol. 1. p. 50,) gives the following estimate of 

 the future resoui'ces of the Bristol Coalfield, which was confirmed 

 by Mr. Cossham at the last meeting of the British Association. 

 Quantity of Coal at a less depth than 1500 feet= 1,718,791,280 tons 

 do. atadepthbetweenl500&3000 „ =1,519,997,981 „ 

 do. do. do. 3000 «& 6000 ,, =2,227,531,577 „ 



do. do. do. 6000 & 8000 „ = 637,990,144 „ 



Total— 6,104,310,982 tons 



Isow as Mr. Hunt says (Min. Stat. 1869,) that our annual 

 output from 34 Collieries is 1,000,000 tons, it follows that our Coal 

 supply is sufficient to last us 6000 years ! In most specimens of 

 our ordinary bituminous coal the vegetable structure is with 



