M^ PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



bighshire, but probably still deeper, and both opening out to the 

 eastward at much greater depths than in the space between them, 

 supposing always the-whole surface defined by an ideal contempo- 

 raneous stratum pervading the whole region. The general synclinal 

 trough of the Principality descends directly into the northern de- 

 pression of Denbighshire, but is separated from that of the South 

 Wales coal-basin by a strongly marked anticlinal ridge. 



In the portion of S. Wales between the great antichnal of the 

 ToAvy and the coast of Cardigan Bay, faults equal either in magni- 

 tude or number to those of N. Wales have not been observed. The 

 folds of the strata are more unbroken, and form regular anticlinal 

 and synchnal hues, which follow a law exactly similar to the anti- 

 clinal of the Towy. In proceeding towards Pembrokeshire, they 

 change gradually and continuously from their south-westerly to the 

 westerly direction which they attain near their southern extremities. 

 lu the great Coal-basin of S. Wales, the faults which have been de- 

 tected are principally perpendicular to the strike, and are therefore 

 transverse faults. They are numerous, and principally along the 

 borders of the basin. Analogy, however, would lead us to infer that 

 characteristic longitudinal faults must probably exist also in the centre 

 of the basin, where the coal-beds on account of their greater depth 

 are less worked, and consequently the geological structure less per- 

 fectly known than near the boundaries of the field. 



In the North of England the geological structure of all the Cam- 

 brian and Silurian rocks is very regular. They present one imiform 

 N.E. and S.W. strike. The Old Red Sandstone does not exist in 

 continuous beds, but only in patches of rough conglomerate. The 

 Carboniferous Limestone rests unconformably on the inferior beds, 

 and has been so elevated that any continuous stratum fonns a surface 

 which we may follow in imagination as we have already done in Wales 

 and the neighbouring district. From Derbyshire to Northumber- 

 land such a surface descends towards the east from a central ridge, 

 which is sometimes an anticlinal line from which our supposed sur- 

 face dips rapidly to the west, or along which it is discontinuous on 

 account of enormous faults bounding the limestone districts on the 

 west. North of Stainmoor the fault assumes the direction of about 

 N.N.W., those in the southerly part of the district being nearly N. 

 and S. The region east of the central ridge is also traversed by 

 numerous transverse dislocations, the general direction of which is 

 east and west. On the west of the central ridge, our supposed sur- 

 face would form a projecting eminence in the Lakes district of West- 

 moreland and Cumberland, terminated by a complete apse at its 

 western extremity, and having a general east and west direction, and 

 therefore nearly at right angles to the central ridge above mentioned. 

 To ihe north of the Lakes and the west of Cross Fell, and to the 

 south of the Lakes and west of the central ridge of Yorkshire, the 

 same limestone-bed descends beneath the existing terrestrial surface. 



The whole of this region from Northumberland to Derbyshire, and 

 on the east of the great central ridge of the north of England, pre- 

 sents that character of continuity in its general structure which na- 



