COAL-MEASURES OF ENGLAND. 435 



parative structure of the carboniferous group in the south of 

 England and South "Wales, Derbyshire, and Yorkshire. 



South of England. ; Derbyshire. Yorkshire. 



" Coal Formation, Millstone 

 Grit, Yoredale Rocks, 

 Scar Limestone, alter- 

 nations of Red Sand- 

 stones,Clays,and Lime- 

 stone ; Red Sandstone, 



n i r< i- ii/r-n ( Coal Formation, Mill- 

 Coal Formation Mill- & ^ Q Q ' Lime _ 



* Gni Ot r 



stone Shale, Moun 

 thick). Mountain 4 . . T . ^, 



' 



Sandstone. 



much developed). 



and Conglomerate. 



In the upper part of the coal measures in Shropshire, a 

 fresh- water deposit extends for about 30 miles, and in Coal- 

 brook Dale a fresh-water deposit containing the shells of 

 TTnio, a river mussel, is found to alternate with a marine 

 bed containing Spirifera and Nautilus. Analogous con- 

 ditions have been found in Yorkshire and Scotland. 



It will be seen that the coal forms but a relatively small 

 part of the formation to which it gives its name, since it 

 occurs in comparatively thin seams, amid masses of rock of 

 far greater size and extent. 



In addition to the remarks already suggested on the 

 importance of coal, we may observe that its value, in 

 this country, is enhanced to an incalculable extent by its 

 association with beds of iron-ore occurring in the con- 

 tiguous shales ; while these, again, could not be fused 

 without the aid of limestone, whfch acts as a flux, and 

 promotes the speedy reduction of the ore. In other 

 countries, where the beds of coal are not accompanied by 

 like deposits, as in Silesia, where they are associated with 

 rocks of older date, and in various parts of Prance, where 

 the coal is similarly situated, its value is restricted to its 

 mere employment as fuel; these countries are thus de- 

 prived of the commercial advantages which we enjoy 

 from its favourable distribution in the British Isles. 



THE COAL-FIELDS OF ENGLAND AND WALES. These are 

 arranged by Conybeare and Phillips, into 



I. The coal-fields north of the Trent, comprising those of 



1. Northumberland and Durham. 



2. Yorkshire, Nottinghamshire, and Derbyshire. 



3. North Staffordshire sometimes called the Pottery coal- 

 field. 



F F 2 



