80 



CARBONIFEROUS SYSTEM. — INTRODUCTION. 



Coal Brook Dale. The account of this, the most productive of the Shropshire coal- 

 fields, will naturally follow, to show, that the thin or upper coal measures of Shrews- 

 bury, reappearing in this tract, are underlaid by lower and thicker carbonaceous 

 masses, containing many beds of valuable coal. Descriptions of the other detached 

 coal-fields of Shropshire will then be given in the following order. The Clee Hills ; 

 The Forest of Wyre, or Bewdley, and Oswestry. 



Quitting the Salopian fields, and passing to the south, the small district of Newent, in 

 Gloucestershire, will claim a brief notice ; but the important coal basin of the Forest 

 of Dean will not occupy attention farther than by occasional references, since it has 

 been adequately illustrated by Messrs. Buckland and Conybeare, aided by the local 

 knowledge of Mr. Mushett 1 . 



South-Welsh Coal-field, (Glamorgan, Monmouth, Brecon and Caermarthen) . No 

 detailed account will be given of any part of this valuable and rich basin, which has 

 been long under the examination of the Rev. W. Conybeare, for whose memoir every 

 geologist is looking with impatience ; but the boundaries of this tract will be alluded 

 to, their eastern, northern and western outlines having been accurately laid down on 

 the map, to indicate the great disruptions along the margin of the basin, and to show 

 the vast expansion of the carboniferous limestone between the South Welsh and 

 Bristol coal-fields. 



We shall then proceed to the consideration of the Old Red Sandstone and Silurian 

 rocks ; the description of the coal-fields of Pembroke and Dudley being deferred to 

 future chapters, as the carboniferous strata in these tracts are so intimately connected 

 with the older rocks, that the history of the one would be unintelligible without a pre- 

 vious acquaintance with the other. In this manner, after a regular examination of the 

 whole succession of rocks, the complicated tracts of Pembrokeshire and Dudley, in 

 which so many different members of the series are intermixed, will be the more easily 

 explained ; clear comparisons being established between them, and unequivocal strata 

 in other parts. Thus carrying down our observations in descending order, the reader 

 will be first familiarized with the nature of those coal-fields, which, although they have 

 hitherto met with little attention, are not only of geological, but also of national in- 

 terest ; for as they are overlaid by the New Red Sandstone, so they may hereafter be 

 worked from beneath that system in several of the central counties. 



But besides the regularly stratified deposits of shale, coal, sandstone, grit, and lime- 

 stone, of which they are composed, some of these coal-fields are perforated by trap 



1 The outlines of this remarkable coal basin, so symmetrically surrounded by zones of millstone grit, carbo- 

 niferous limestone, and Old Red Sandstone, will be seen by reference to that part of the map which has been 

 coloured from the original work of Mr. Maclauchlan, of the Ordnance Survey, now deposited in the collection 

 of the Geological Society. I am indebted to this gentleman for much valuable information concerning this and 

 other adjacent tracts, and particularly in the delineation of the outline of a large portion of the South Welsh 

 coal-field, with the topography and geological structure of which he is most intimately acquainted. 



