488 PLEISTOCENE. 



angular drift with fewer glaciated stones : many sections show an alternation of 

 contorted beds and undisturbed strata. Mr. Goodchild concludes that while the 

 whole district, to a height of about 2400 feet, was enveloped in a portion of a great 

 ice-sheet, formed of ice partly from Scotland and partly from the Lake District, and 

 adjoining uplands, yet the drifts were mainly accumulated afterwards by the melting 

 of this covering, and the consequent liberation, as a sediment, of the stones, sand, 

 and mud that had been dispersed throughout the ice. Much of the surface-con- 

 figuration of the Dale-district was due to the modification of pre-existing features 

 by Glacial erosion.^ 



In North Lancashire and adjacent parts of Yorkshire and Westmoreland 

 evidences also of widespread and almost universal glaciation were previously 

 recorded by Mr. R. H. Tiddeman. There the general movement of the ice was 

 to the south across deep valleys and over hills of considerable elevation, its 

 direction being modified by ice from the Lake-district. Stripe were not observed 

 at heights over 1500 feet. Regarding the Till in this area as the product of an 

 ice-sheet, Mr. Tiddeman has observed that there is abundant evidence that it is 

 not coloured by the rocks on which it lies, but by the rocks over which it has been 

 pushed ; and that it is quite possible, nay certain, that in some areas there may be 

 beds of Till of totally different appearance, colour, and material, deposited side 

 by side, by the same agents, and under the same conditions, at the same time.^ 



In West Cumberland, Lancashire, parts of North Wales, and Cheshire, the 

 Drift deposits have been divided as follows : — 



Upper Boulder Clay 20 to 100 feet. 



Middle Drift (sand and gravel) 10 to 200 ,, 



Lower Boulder Clay 20 to 120 ,, 



The total thickness is rarely more than 150 to 200 feet. The beds were first 

 divided in the neighbourhood of Manchester by Prof. E. Hull. The Upper 

 Boulder Clay consists of reddish-brown clay, with grey and blue partings, and 

 glaciated stones and boulders. It sometimes contains bands of sand and finely- 

 laminated clay. It may be seen at Ormskirk, Wigan, Lancaster, etc. There 

 are many old marl pits over the area occupied by this Clay, and it has been 

 worked for brick-marking at Blackpool, Preston, Blackburn, Croston, and 01 her 

 places. 



The Middle Drift consists of fine sands and gravel with subordinate beds of clay 

 and loam, the whole in general distinctly stratified, but frequently contorted. 

 The maximum thickness in Cumberland is about 120 feet; at Gresford, near 

 Wrexham, 150 feet ; at Kersal Moor, Lancashire, 200 feet. In many places 

 it contains fragments of marine shells in abundance. (See sequel.) 



The Lower Boulder Clay consists of stiff reddish-brown clay, with subordinate 

 beds of laminated loam, seams and pockets of sand, stones nnd many large 

 boulders. This, according to Mr. Mackintosh, graduates into a harder and more 

 stony clay "with a tendency to arched stratification in the neighbourhood of the 

 hills"; it is known as " Pinnel " in Furness. Its thickness at Lindal, Furness, 

 is about 120 feet. The lowest portion of the accumulation is a blue or bluish- 

 grey stony clay, with many scratched boulders. This Boulder Clay is also largely 

 used for brick-making. 



All the divisions, according to Mr. Mackintosh, are locally shelly, excepting the 

 'Pinnel,' and the lowest blue Boulder Clay.'^ The most abundant shells are 

 fragments of Tellina BaliJiica, Cardiiim edtile^Astarte borealis, and Tiirritella terebra. 

 The Boulder Clay contains blocks of granite, and various eruptive rocks, grits, 

 slate, Carboniferous Limestone, etc. Chalk-flints have been found in the Drift 



^ Q. J. xxxi. 55. See also J. W. Davis, G. Mag. 1879, p. 313; W. Gunn, 

 Ibid. p. 384. 



* Q. J. xxviii. 471, 485. 



^ See Daniel Mackintosh, G. Mag. 1870, p. 445, 1871, pp. 250, 303, 1S72, pp. 

 IQO) 399 ; Q- J- XXV. 407, xxviii. 391, xxx. 174, xxxiii. 730, xxxvii. 351 ; G. H. 

 Morton, Geol. Liverpool, 1863. 



