But great and valuable as this section shews the Mid-Lothian 

 coal-field to be, it only comprehends the class of Edge-Coals on 

 both sides of the coal basin with the underlying bed of lime- 

 rock. None of the very valuable coals, termed the Flat Coals, 

 which chiefly supply Edinburgh, are comprehended in it ; for 

 hitherto the strata betwixt the upper coals in the section and the 

 flat-coalsj which lie above these, have not been accurately ascer- 



