138 
which crack or divide into irregular columnar appearances, 
although larger and more expanded, somewhat agreeing also 
with the mineral coke—see tab. 192 :—but as. they are also 
more compact, it may depend upon the substances around 
them preventing in a great measure their expansion, which 
would agree in some measure with the experiments made by 
the ingenious Sir James Hall. 
A long time since I received a portion of columnar 
Glance Coal from a Dyke about ten miles from Wanlock- 
Head, by favour of G. Laing, Esq., which so nearly re- 
sembles this in structure and appearance, that thence we 
might suppese them the same thing; and Mr. Greenough 
has specimens which are more intermediate, some parts 
having Plumbago about them. 
