224 TRANSACTIO>S OF THE [mAR. 15, 



THE LANCASHIRE COAL FIELD. 



By Herbert Bolton, F. R. S. E. 



Assistant Keeper, The Manchester Museum, Owens College. 



CONTENTS, 



1. Topographical Features 224 



2. Superficial Deposits : 225 



3. Mining History 225 



4. Millstone Grit Series 226 



5. Lower Coal Measures 228 



6. Middle Coal Measures 230 



7. Upper Coal Measures 237 



8. Post Carboniferous Changes 239 



9. Flora 241 



10. Fauna 245 



Topographical Features. 



The topographical features of the Lancashire Coal field are 

 well marked. On the south and west it is bounded along a line 

 of faulting, by the low Triassic plain of Cheshire and western 

 Lancashire. Along the northern and eastern sides it is shut in 

 by a series of loft}' moorlands covered by extensive peat de- 

 posits and overgrown with heather. 



The flanks of the moorlands are deeply gashed by narrow ra- 

 vines called " doughs," the sides of which, clothed with the 

 bracken and other ferns, lodge a few hardy trees and shrubs. 

 Here and there the ravines have vertical walls of massive grits. 

 The whole of this area consists of Millstone Grit rocks, which 

 were elevated into anticlines during Mesozoic times. 



At the base of the highest moorlands are low rounded foot- 

 hills whose sides and crests are clad with trees or mapped out 

 into grazing farms. These hills consist of the upper members of 

 the Millstone Grit, or of the Lower Coal Measures in which grit 

 rocks are a strong feature. The hill slopes are usually steep. 

 Most of the mining of the Lower Coal Measures is done by means 

 of" adits " which pass into the sides of the hills or else by shal- 

 low shafts which do not exceed 100 yards in depth. 



The southern fringe of the coal field might be described as 

 a hummocky country, a series of shallow river valleys sepa- 

 rated by low, broadly rounded hills. It is along this southern 

 fringe that the rich Middle Coal Measures chiefly occur, only 

 a few isolated patches being found in the northern half, the chief 

 of which is known as the Burnley coal basin. 



