AND RECENT GRAVELS NEAR MANCHESTER. 455 



It also forms outliers over the Cheshire plain, as at Bowdon 

 and High Leigh. Near its margin it often appears to thin 

 away rapidly _, the Upper Till descending to meet the Lower, 

 as in the case at Cheetham Hill, mentioned by Mr. Binney. 

 Such accidents I am disposed to refer to the period of the 

 last denudation of the country, when these post-pliocene 

 deposits were very largely removed by the waters of the 

 retreating sea. The sand being extremely soft and porous, 

 the sea along the margin would penetrate inwards to some 

 distance, and, forming a running sand, might wash it away 

 much more rapidly than the Upper Boulder-clay, which, 

 from its stiff and plastic nature, would to some extent with- 

 stand the action of the waves. 



The Middle Sand is, unfortunately for its consistency of 

 character, not always free from bands of loam or clay. 

 One of these, which is largely used for brick-making near 

 Prestwich, Heywood, and Rochdale, occurs about the 

 centre of the mass, and divides the sand into two members, 

 the upper of which frequently occurs in detached hillocks. 

 This bed is, however, of very local occurrence, and thins 

 out southward. 



It is very probable, if not positively certain, that the 

 Bisplam gravels, described by Mr. Binney (1861) as con- 

 taining nineteen species of shells now living in the Irish 

 Sea, belong to this division. Shells are also abundant in 

 it at Macclesfield. 



The Upper Boulder -clay , or Till. — This member caps the 

 sand over the flat ground extending from Stockport to 

 Alderley. Amongst the hills of the Pennine Chain to the 

 east, it frequently occupies the valleys, as at Broadbottom, 

 New Mills, Chapel-en-le-Frith, and Saltersford. It occu- 

 pies the districts of Haughton Green and Hyde, Denton, 

 Newton, Fairfield, Failsworth, Hollinwood, Oldham, and 

 the higher parts of Harpurhey and Blackley. It also forms 

 a capping for the sand along the Irwell, from Pendlebury 



SER. III. VOL. II. 2 H 



