COAL-FIELD OF CLACKMANNANSHIRE. 147 



direction, Fig. 1. Plate VIII. represents an exten- 

 sive district of country, containing a coal-field di- 

 vided into numerous subordinate coal-fields, by 

 'these dislocations. The lines marked b are slips; the 

 broad lines marked c represent dikes : the former 

 dislocate the strata, the other, viz. the dikes, only 

 separate the strata the thickness of the dike from 

 each other. The two parallel lines marked a, repre- 

 sent two seams of coal, variously thrown up and 

 down by the slips ; whereas the dikes pass through 

 the strata without altering their position. In this 

 manner, coal-fields extend over a district of country 

 to the extent of many miles in every direction. 



The only exception which I have observed from 

 this form of the coal-fields in Great Britain, is the 

 Inverted Bason-shape, and this comparatively very 

 seldom occurs : examples of it, however, are to be 

 seen in Fife, and in several districts in England ; 

 but even in extensive coal-fields, the inverted ba- 

 son-form is only a partial occurrence, or a deviation 

 from what we conceive to be the general and or- 

 dinary form. Fig, 1. Plate VI. is an example 

 of this formation of the coal-field, as it exists in 

 Staffordshire, at the Castlehill, close to the town of 

 Dudley, upon which Dudley Castle is built. 

 Through this hill, canals have been cut for working 

 the great beds of limestone, and in it immense ex- 

 cavations have been made. These beds of lime- 

 stone are found in the lower series of the strata of 

 the coal-field, and of course are to be found at many 



K 2 



i 



