1872.] MACKINTOSH — CHESHIRE BOTJLDER-CLAY. 389 



shaved off before the upper clay was deposited. Neither the fractures 

 of the latter, nor the light-grey or bluish substance (carbonate of lime) 

 "with which they are faced, descend into the lower clay. This sub- 

 stance gives a character to the upper or brick-clay all round the 

 shores of the Irish sea as far north at least as Barrow, and as far 

 west as, if not further than Colwyn. In the lower clay, at Dawpool, 

 a very few instances, on a small scale, of grey partings may be 

 detected; but they consist of sulphate of lime, and can often be 

 traced to the decomposition of fragments of gypsum imbedded in 

 the clay. 



On breaking into the upper clay, its colour in the Dawpool sec- 

 tion is a peculiar brown ; elsewhere its colour (apart from the grey 

 or blue facings) is often reddish or reddish-brown, especially when 

 seen from a little distance. The lower clay is rather darker and 

 brighter, and varies from a chocolate-brown to a madder-brown. 

 The upper clay contains few stones, and still fewer boulders. In 

 the lower clay the stones increase in number downwards until it is 

 nearly pack-full of them towards the lowest visible part of the sec- 

 tion. The structure of the upper clay (with the exception of the 

 far-travelled stones) indicates nothing further than ordinary sedi- 

 mentary deposition. The lower clay is charged with grit and stones 

 from the size of a pin's head up to good-sized boulders and (at the 

 base of the deposit) enormous blocks. Its structure exhibits no 

 traces of its component parts having been assorted by the ordinary 

 action of water, excepting the frequent occurrence of a series of 

 horizontal and parallel cracks, which would seem to point to succes- 

 sive deposition*. The lower clay is harder than the upper. It re- 

 sists the softening influence of water, and stands after being under- 

 mined. It has even admitted of caves being excavated in it by the 

 sea. The upper clay will not stand when overhanging, or indeed 

 for any considerable time at an angle of more than 25° or 30°. It 

 is so easily softened by rain-water that its presence in railway cut- 

 tings can generally be safely inferred from the frequent appearance 

 of landslips. In the upper clay the fractures are vertical ; in the 

 lower they cross each other obliquely, and are intersected by gaping 

 parallel joints which are inclined from the perpendicular at an 

 angle of from 15° to 20°. 



The lower clay is as much a glacial clay as any I have yet seen. 

 It is evidently on the same horizon with the Lower Boulder-clay 

 which at intervals may be seen along the coasts of the Irish Sea 

 from "Workington to Anglesea. It differs from the pinnel of Fur- 

 ness and the central parts of the Lake district, in the pinnel being 

 still more charged with stones, in these stones being very much less 

 polished and striated, and in the pinnel exhibiting a tendency to a 

 curved or arched stratification. 



The majority of the stones in the lower clay at Dawpool are more 

 or less glaciated on one or two sides, or all round. The striae in 

 many instances run parallel; in others they cross each other at 



* It likewise contains seams and pockets of sand, and, in one or two places, 

 may be seen graduating into, or replaced by, a nearly stoneless clay or loam. 



