630 



STRATIGRAPHICAL GEOLOGY 



with grey and in containing fewer stones. A 

 good section of these drifts is exposed in the 

 cliffs near Blackpool and is represented ' in 

 Fig. 205). 



Both the boulder-clays and the sands fre- 

 quently contain marine shells, generally broken, 

 but sometimes perfect, and also abundance of 

 Foraminifera. Moreover, the Gastropod shells 

 are seldom filled with clay or red sand, but 

 generally with a fine white sand or silt which 

 is full of Foraminifera, showing that they have, 

 been picked up by the ice from silty shores and 

 sea-bottoms, and these silt-filled shells are just 

 as common in the boulder-clay near Macclesfield, 

 at 600 feet, as they are near the, coast. Near 

 Macclesfield, too, there are sands with the same 

 species of shells at a height of 1200 feet above 

 the sea. 



The stones and boulders in these clays have 

 come principally from the Lake District and the 

 south of Scotland. They include granite from 

 Eskdale and granophyr from Butterniere, other 

 granites from Galloway, rocks from the Borrow - 

 dale Volcanic Series, Silurian Grits, and Carboni- 

 ferous limestones. Mixed with these in smaller 

 numbers are blocks of Triassic sandstone and 

 flints, which latter must have come from Antrim 

 or from the west of Scotland. The finer material- 

 has, however, been largely derived from the 

 Triassic sandstones and clays which underlie the 

 Glacial deposits, and doubtless extend far to 

 the west and north-west below the floor of the 

 Irish Sea. 



These deposits fill up and conceal the in- 

 equalities of a deeply sculptured pre-Glacial 

 surface. The lakes of Coniston and Windermere 

 are merely the upper ends of pre-Glacial valleys, 

 the lower reaches of which are filled with Glacial 

 drift, and where these old valleys open into 

 Morecambe Bay the valley bottom is probably 

 200 or 300 feet below the present sea- level, 

 for in Furness one such valley descends to 

 460 feet below sea-level and is filled with drift. 



Southwards these deposits sweep over the 



