436 SPECIAL GEOLOGY. 



4. Manchester. 



5. Whitehaven. 



II. The Central coal-fields, including those of 



1. Leicestershire. 



2. North Staffordshire. 



III. The Western, divided into 



1. The North-western, containing those of North Wales. 



2. The Western, comprising those of the Plain of Shrews- 

 bury ; of Coalbrook Dale and the Glee Hills. 



8. The South-western, comprising the coal-fields of South 

 Wales, of the Forest of Dean, and those of Gloucestershire 

 and Somersetshire.* 



Coal also exists in Prance, the Netherlands, the banks of 

 the Rhine, in Saxony and Bohemia, in Sweden and Russia, 

 in Persia, China, and Hindostan, in North and South 

 America, and Australia, 



IGNEOUS HOCKS. These are frequent in the carboniferous 

 group of this country, occurring as overlying stratiform 

 masses alternating with sedimentary deposits ; but more 

 frequently as dikes, which have penetrated through the 

 strata. In England, the principal intrusions of these 

 rocks consist of greenstone and basalt, locally termed whin- 

 stone in the North of England ; the toadstone of Derbyshire, 

 so called from its mottled appearance; and the basaltic masses 

 of the South Staffordshire or Dudley coal-field belong to these 

 rocks. The dikes exhibit the effects usually observed at the 

 point of contact of rocks of this character with sedimentary 

 deposits, especially that of hardening and crystallising them, 

 converting shale into slate, charring coal to coke, anthracite, 

 and plumbago, and inducing crystalline texture in lime- 

 stones and calcareous rocks. 



VEGETABLE ORIGIN OF COAL, The vegetable origin of 

 this substance is now admitted, and no doubt exists, that 

 it consists of the vegetation of the ancient earth, which has 

 been buried beneath waters, and has either been submerged 



* Mr. Sopwith has executed some beautiful models, which exhibit, in the 

 most instructive manner, the stratification of the coal and the accompanying 

 deposits; and has thus depicted the coal measures of the Forest of Dean, by 

 means of sliding tables, which display the amount of coal, both wrought and 

 unwrought, as well as of the ironstone which accompanies it. These models 

 may be procured of Mr. Tennaut, No. 149, Strand. 



