528 NORTHERN DRIFT CONTAINING SEA SHELLS OF EXISTING SPECIES. 



Northern Drift, containing Granite Bowlders and Sea Shells of existing species. 



The region thus partially occupied by local detritus, derived from various centres, is 

 overspread by a great drift from the north, which, as has been already stated, covers 

 large tracts of Lancashire, Cheshire, Shropshire, Staffordshire and Worcestershire. 

 The country from which this drift proceeded is clearly shown by its contents, for none 

 of the varieties of granite and other rocks which it contains, occur in Wales or the 

 adjacent parts of England, but they are all well known to exist in Cumberland and 

 Scotland. This granitic detritus is further proved to have issued from the north, not 

 only by its greater volume in that direction, but also by the blocks diminishing gra- 

 dually in size as they are traced from north to south. On or near the coast of Lan- 

 cashire (as at Preston) 1 the thickness of the drift is 150 feet and more, consisting, in 

 some parts, of deep masses of clay, in others of sand and fine gravel, in all of which 

 large bowlders of granite are mixed up with some local detritus and sea shells of exist- 

 ing species. The drift thus characterized (and traceable almost every where by its 

 granite bowlders on or near the surface) covers a very large portion of Cheshire and 

 the adjacent tracts of Staffordshire and Shropshire ; thus ranging over nearly the 

 whole region coloured as New Red Sandstone with patches of coal measures. On 

 the east it has no well-defined limit that I have yet observed, until it reaches the vale 

 of Worcester, where it occurs in the form of a delta, included between the Silurian 

 hills on the one side and the Cotteswolds on the other ; both of those hilly ranges 

 being entirely free from it. The greater part of its western flank is clearly defined. 

 Advancing from the low country, south of Liverpool, it has swept across Flintshire^ 

 but has been arrested on the edge of the North Welsh mountains 2 . On Moel Tryfan 

 it occurs at nearly 1750 feet above the sea. The chain of mountain limestone and mill- 

 stone grit, constituting the edge of the high lands of Denbighshire, seems to have been 

 the ancient shore of this drift 3 . Near Wrexham it forms masses of vast thickness, con- 

 But this is not the case, for their transport took place during the accumulation of the deposits in which they 

 were imbedded, previously to the action of the waters, which formed the superficial drift and only loosened 

 them from their parent bed and moved them a short distance. 



1 I communicated some of my views concerning this northern drift, as seen at Preston and other places, to 

 the first meeting of the British Association, September 1831, and I inferred, from the phenomena which I had 

 then noticed, the recent elevation of large portions of the island. See LyelFs Principles of Geology, vol. i. 

 p. 269, and Map. The area over which I have examined the phenomena has since been very widely extended. 



2 Mr. Trimmer first called attention to the sea shells and coarse granitic gravel on Moel Tryfan, 1692 feet 

 above the sea. 



3 Mr. Bowman, of Gresford near Wrexham, has favoured me with some valuable details concerning the 

 structure of the drifted materials in that neighbourhood. He has detected as many as 13 different varieties of 

 granite, mixed with other rocks of northern origin, and a great proportion of fragments derived from the adjacent 

 grits and limestones and slaty rocks. Mr. Bowman read an interesting memoir on the Cefn Caves to the 

 British Association at Bristol, 1836, which has not yet been printed, in which he treats incidentally of this 



