6 
THE CARBONIFEROUS VOLCANOES 
BOOK VI 
dolerite, coming evidently from an easterly quarter, has broken up and 
thrust itself beneath a bed of limestone. Again, when the sill bifurcates 
the branches unite towards the east or north-east . 1 The sill can be proved 
to thin away to the west from Teesdale to the Pennine escarpment, and in 
1 Op. cit. p. 415. 
