44 



GEOLOGICAL HISTORY. 



[CH. 



The usual classification adopted for the British Coal- 

 Measures is that of Upper, Middle, and Lower Coal- Measures; 

 l^etvveen the Upper and Middle divisions there occur certain 

 transition or passage beds which are known as the Transition 

 series. Continental writers, and more recently Mr Kidston of 

 Stirling, have attempted with considerable success to correlate 

 the Coal-producing strata by means of fossil plants^ 



10 in. ^ 



lOiin 



Massive clay-shale with a few 

 coal films in the lower part. 



Shale full of thin streaks of 

 coal. 



Massive shale with a few streaks 

 of coal and iron pyrites. 



Bastard coal ; more coal than 

 shale. 



Good coal, with masses of iron 

 pyrites. 



Coal and seat-rock mixed. 

 Seat-rock. 



Fig. 4. 



Vertical section of the Bassey or Salts Coal seam, Rushton Colliery, 

 Blackburn (Lower Coal-Measures). From a specimen 4 feet 4 inches in height, 

 presented by Mr P. W. Pickup to the Manchester Museum, Owens College. 



Finally, some reference must be made to the occurrence of 

 Carboniferous rocks underneath more recent strata. In a 

 geological map, or bird's-eye view of a country, we see such 

 rocks as appear at the surface; by means of deep borings, 

 however, we are occasionally enabled to follow the course of 

 older beds a considerable distance below the usually accessible 



1 Kidston (94). 



