AROUND THE ESTUARY OE THE DEE. 737 



of such around the estuaries of the Dee and Mersey. Even on Hope 

 Mountain the apparently mamillated form of the surface is chiefly 

 the structure of the beds of Millstone -grit developed by denudation. 

 Horizontal and Vertical Hang e of the two Boulder-clays of the Basin 

 of the Irish Sea. — These two Boulder -clays are often separated over 

 large areas by middle sand and gravels, as proved by the geological 

 surveyors in Lancashire, and as may be seen in Cumberland between 

 the estuary of the Duddon and llavenglass (Geol. Mag. for June 

 1871). To the south of the Mersey the upper clay is generally 

 found lying on the surface of the middle sand ; and, excepting in 

 hollows, there is very little lower clay further south than Chester, 

 though, under the middle sand, it is often represented by a loam 

 with erratic stones, but without shells, which would appear to be 

 the equivalent of the base of the formation further north. In many 

 places in Shropshire this loam is the only drift-deposit. The small 

 quantity of typical lower clay south and south-east of Chester may 

 be accounted for partly by supposing a southerly diminution in the 

 supply of subglacial clay, and partly by the evident using up of the 

 stony contents of the lower clay during the accumulation of the 

 middle drift which, for a great distance south and south-east, con- 

 tains lower-clay erratics. 'The lower clay is much the same along 

 the shores of the Irish sea from the Solway Frith to the neighbour- 

 hood of Chester, and from that neighbourhood to Anglesey, as I 

 have had many opportunities of ascertaining. The upper clay is 

 likewise the same from the banks of the Eden, near Carlisle, to 

 Crewe in Cheshire, and from Crewe to Anglesey. The greyish- 

 faced fractures are not always present ; but they frequently recur. 

 At the Dalton brick-pits, Barrow-in-Eurness, and at Crewe, they 

 impart a general bluish-grey colour to the clay ; and all the way 

 between these two places they may often be seen. They likewise 

 frequently recur in Shropshire and Denbighshire. They resemble 

 the ash-coloured partings of the Hessle clay described by Mr. Searles 

 Y. Wood, jun. As regards vertical range, the lower clay nowhere, 

 so far as I have seen, maintains its low-level or shelly character at 

 a greater height than from 100 to 150 feet, as Mr. De Bance long 

 ago pointed out ; but it is certainly continuous with a deposit of 

 mixed loam, clay, and gravel which runs up the hill-sides to a great 

 altitude. I have never seen typical upper clay at greater heights 

 than from 400 to 600 feet ; and it generally loses its shelly character 

 before it reaches these heights. Mr. S. Y. Wood, jun., has not found 

 the Hessle clay (with which he is disposed to correlate the north- 

 west-of- England upper clay) at a greater height than about 300 feet 

 in Yorkshire, while in South Lincolnshire it does not reach higher 

 than about 50 feet above the sea-level. The upper clay of the 

 north-west does not penetrate into the valleys of the Lake-district, 

 or into the valleys of Wales, with the exception of the Yale of 

 Clwyd and the valley traversed by the Mold-and-Denbigh railway, 

 in which it does not rise to the level of the water-parting. On the 

 east slopes of Halkin Mountain it thins out upwards at about 400 

 feet, and east of Glossop at about 600 feet. 



