AND RECENT GRAVELS NEAR MANCHESTER. 457 



As an illustration, let us take the lower boundary of the 

 Upper Boulder-clay along the valley which runs up from 

 Manchester_, by Bolton, to beyond Sharpies, and examine 

 the levels as taken from the Ordnance 6-inch maps. At 

 Pendlebury the base of the Upper Boulder-clay is 275 feet 

 above the sea-level; at Clifton, 285; at Kearsley, 300 ; at 

 Halshaw Moor it descends again to 285 ; opposite Burnden 

 Bridge it again reaches 300; at centre of Bolton, 300; Little 

 Bolton, 370 ; the banks of the Tonge and Bradshaw brooks, 

 near Bradshaw Bridge, 380; Sweetlove's Colliery, Sharpies, 

 475 ; and still further north, at Holmes Farm, above 

 Dunscar Bridge, 500 feet. Thus, in a distance of about nine 

 miles along this valley, the base of the Upper Boulder-clay 

 has ascended from 275 to 500 feet, that is, by an amount of 

 225 feet. The rise is therefore — ^^-, or 25 feet per mile. 



A similar rise is observable, if we take the section of 

 country from Manchester to Oldham, or from Manchester 

 to Dukinfield. Thus at Gorton the level of the base of 

 the Upper Boulder-clay is 250 feet, and at Dukinfield (as 

 may be determined at the sand-pit near St. John's Church) 

 it is about 480 feet, being a rise of 230 feet in four miles. 

 That there is a similar slope towards the valley of the 

 Mersey from the Cheshire hills is proved by the position of 

 the beds along the brook-courses, as already stated. 



The different members of the Drift series rest indis- 

 criminately on the older rocks, which were worn into hills 

 and valleys, or plains, before their deposition (see fig. 3) . 

 Thus in Manchester the Lower Boulder-clay rests on the 

 Triassic and Permian beds; but at Heywood, Bochdale, 

 and Dukinfield the older rocks are covered by the Middle 

 Sand; and all along the rising ground of the lower Coal- 

 measures, from Oldham by Staleybridge, Marple, and 

 Difeley, the Upper Boulder-clay rests upon, or has been 

 deposited against, the steeply sloping sides of the Carboni- 

 ferous rocks. 



3 II 2 



