DU NOYER — BITUMINOUS COAL OF THE ARIGNA DISTRICT. 83 
flaggy grits of the basal 
coal-measures. Above this, 
and forming the rugged 
scaur on the brow of the 
mountain, are the " Bottom 
Sandstones," or seat-rock 
of the coals ; above them 
are the two coal-beds ; the 
" crops " of which are de- 
fined hj the level surface 
of the underlying sand- 
stones, at either side of the 
mountain. 
The summit is formed of 
sandstones, with dark grey 
shales, flaggy grits, and 
some nodular bands of clay 
ironstone (see Section). 
The mountain to the 
extreme right is Altagow- 
lan, and the two coal " crops' ' 
near its summit are clear- 
ly defined on its northern 
side, by the low precipitous 
faces of the sandstones 
with which the coals are as- 
sociated. 
By reference to the ac- 
companying Sections, Nos. 
1 and 2, the physical struc- 
ture of both these moun- 
tains will be at once under- 
stood. 
In order to afford a still 
clearer notion of the vast 
amount of denudation to 
which the whole of this dis- 
trict has been subjected, I 
give the subjoined diagram- 
matic section across it, from 
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