244 PHYSIOGRAPHY. [chap. 



insignificant quantity at Bovey Tracey in Devonshire, but 

 in many countries, which are poor in true coal, the lignite 

 occurs in large deposits and is an important fuel. A few 

 years ago, some old timbering in a mine in the Hartz, 

 known to date back about four hundred years, was found to 

 be converted into this lignite or " brown coal." Hence, 

 there can be no doubt that, under certain conditions of 

 decay, wood may be transformed into a coal-like material. 

 Lignite may be regarded as vegetable matter not com- 

 pletely mineralized. Even the ordinary coal of our own 

 country is subject to further alteration, and may" become 

 still more removed in characters from its original condition. 

 Thus, in the coal-field of South Wales, a curious change may 

 be traced in passing from one end of the field to the other. 

 In the eastern part, the coal is of the ordinary kind, such as 

 is seen in our scuttles, and is called bituminous coal ; towards 

 the middle of the field this passes into semi-bituminoiis coal, 

 which is a kind of fuel that does not burn with a bright 

 gassy flame, but is valued for feeding the engines of steamers, 

 since it emits but little smoke ; finally, in the western part of 

 the coal-field, this steam-coal passes into a substance called 

 anthracite^ which is still less inflammable and still more 

 removed from the original form of vegetable matter. Such 

 changes in the character of the coal are connected with the 

 presence of eruptive rocks which have burst through the 

 coal seams. Most deposits of coal have been thrown into 

 basin-like shapes, and the beds are often broken up, and 

 otherwise disturbed, by the presence of igneous rocks. In 

 the neighbourhood of these rocks, the coal has been altered 

 into an anthracitic material. In fact, the alteration which 

 has been effected appears to be much like that which 

 takes place when coal is artificially distilled, for the 

 ' Anthracite, from a,vQfa\, anthrax, coal or charcoal. 



