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 line 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 Yein, 

 Eocky Yein, and Upper and Lower Churchway Yeins. 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 Yeins, 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 Yein, Whittington Delf Yein, Coleford High 

 Delf Yein, and Upper and Lower Trenchard Yeins — the whole 

 thickness about 17 feet. Of these, the Coleford High Delf is 



