174 Reviews — Geology of the South Wales Coalfield. 



an unconformity occurs), and not at the top of that zone. In connexion 

 with this, interesting sections showing contemporaneous piping of 

 mudstones into oolitic limestones of the lower part of the Syringo- 

 thyris zone are described, and the phenomena are illustrated in two 

 plates. 



The Carboniferous Limestone in this area rests conformably upon 

 the Old Hed Sandstone, but is succeeded unconformably by the 

 Millstone Grit: in neither case do we get information about faunas of 

 passage beds between the Carboniferous Limestone and the older and 

 newer strata. 



The Millstone Grit is divided into three divisions, which do not 

 show any features of exceptional interest. 



The Coal-measures are naturally described in great detail. Only 

 the eastern portion of the Pembrokeshire Coal-field is represented in 

 the district of which the memoir under consideration is descriptive. 



The coal-field here is broadly a sj'ncline, but while the various 

 subdivisions lie in normal superposition on the northern side of the 

 trough, the central and southern portions are complicated by inverted 

 folds and an almost infinite number of large and small overthrust 

 faults. The basin here has been involved in two great belts of 

 disturbance. On the south it is touched by the northern margin 

 of the Armorican belt, with overthrusting and overfolding from the 

 south ; on the north it is affected by disturbances which also affect 

 the Old Red Sandstone and Ordovician strata, and show evidence of 

 overfolding and overthrusting from the north ; in the centre there is 

 comparatively little signs of disturbance. 



The coals of this area are all anthracitic. The lower series, and 

 probably only the lower half of that series, of the Coal-measures of 

 Carmarthen and Glamorgan is alone represented in East Pembroke, 

 and it is impossible to correlate with certainty the individual seams 

 of this latter area with those of the former. Three seams have yielded 

 the bulk of the coal, namely, the Rock, Timber, and Lower Level 

 and Kilgelty veins. 



There are no Triassic rocks in the district, but their former presence 

 is indicated by reddening of the Carboniferous rocks. 



Certain vein-quartz pebbles in a subsoil near Coedcanlas are noticed 

 and referred to a possible Eocene date. 



A very interesting chapter on Tectonics follows the description of 

 the strata. The nature of the chief movements and their effects has 

 already been noticed. 



A raised beach overlain in one place by glacial drift corresponds 

 both in position and age with one which occurs at intervals all around 

 the Bristol Channel. 



The glacial drifts are described, and a map on p. 218 indicates the 

 distribution of the boulders and their directions of transport. There 

 are also notices of river-terraces and of a submerged forest. 



A chapter is devoted to economics, and notices lime and limestone, 

 building stone, bricks, roadstone, timber, and water-supply. The 

 character of the coal is dealt with in another memoir. 



Four appendices treat of the fossils and of photographs of geological 

 subjects belonging to the Geological Survey. 



