266 
THE GEOLOGIST. 
field, -which has special interest — geological as well as industrial — 
on another occasion. 
If the ordnance geological sheet N"o. XLIII. S.E. be examined, 
with the horizontal sections Nos. 15 and 16, a very good notion of this 
coal-basin may be obtained, although not too much dependence is to be 
placed, practically, on the position of the lines marking the crop of the 
several veins. Indeed, to lay down the line of crop accurately, in many 
places where there are no workings, is impossible, from the thickness of 
the over-burden or soil : besides which, the theoretical lines invariably 
require to be shifted, from the occurrence of minor faults and local 
denudation. 
The measures may be conveniently divided, in descending order, 
into — 
1. The rock series. 
2. The shale or argillaceous series. The Brazilly vein of coal being 
taken as the Hue of demarcation between the two. 
The Brazilly rock furnishes a free-stone, said to have been quarried 
for the hearths of the charcoal iron-furnaces formerly in use. 
The upper series may be further subdivided by a straw-coloured 
sandstone, thought, by some, to represent the Pennant-rock of the 
Somersetshire coal-fields. 
Adopting the arrangement given, the following will be the order of 
the coal seams : — 
1. Woorgreen's coal : three small seams of an aggregate thickness of 
four to six inches. In the lowest bed of the alternating sandstone 
is found a thin band of ironstone, formerly worked to a small 
extent. 
2. The smith's coal ; Lowrey or Park End High Delf ; Starkey Vein, 
Rocky Vein, and Upper and Lower Churchway Veins. These veins 
alternate with impure sandstones and sandy shales, locally called 
"Cliff" and "Stone-bind." United thickness of these coal-seams, 
about five yards. In the clay between the Starkey Veins, which 
are double, and worked together, argillaceous ironstone is met with, 
but in sparing quantities. The veins in this series extend over an 
area of about 7,000 acres. 
3. The Nag's Head Vein, Whittington Delf Vein, Coleford High 
Delf Vein, and Upper and Lower Trenchard Veins — the whole 
thickness about 17 feet. Of these, the Coleford High Delf is 
