THE FYLDE: GEOLOGY AND PHYSICAL FEATURES 17 



The river Wyre is formed by the union of streams from Tarnbrook and 

 Marsham Fells, and then flows south to Garstang, south-west to Poulton, and 

 finally north to Fleetwood. 



The Pleistocene glacial drift, laid down on a denuded platform, includes 

 Lower and Upper Boulder Clays sometimes distinguishable because Middle 

 Sands and Gravels occur between. The basic study is by De Ranee, who found 

 at Eagberg Brow, Norbreck, a 30 feet high dome of Boulder Clay covered by 

 silt-laminic (3 inches to 5 inches), green and brown or purple, and containing 

 large erratics. The erratics near the top are smaller and layered. The Middle 

 Sands and Gravels are variable, with 2 feet to 4 feet layeis of sand and gravel 

 alternating for some 1 4 feet and a cover of 1 6 feet of sand ; they show current 

 bedding. These Middle Sands were laid down in waters held up in front of 

 the earlier ice-sheet as it retreated, and their undisturbed state shows that they 

 were frozen when the ice bringing the Upper Boulder Clay advanced over them. 



The Middle Sands and Gravel underlie almost the whole of the Upper 

 Boulder Clay of the Fylde, but at several places the capping of the latter has 

 been removed, and the Middle Sands form the present surface. The largest 

 outcrop in the Fylde has an area of about half a square mile, and is midway 

 between Inskip and Elswick, two miles south-south-west of St. Michaels. 

 Two-and-a-half miles west of this, there is another about half the size by the 

 hamlet of Thistleton. The western portion of Kirkham is on Middle Sand, 

 and there are several other very small scattered outcrops. 



In the spring of 1936, owing to imperfections in the grass cover just south of 

 Bispham, the Middle Sands could be seen at the top of the cliff, overlying the 

 Lower Boulder Clay. North of Norbreck, the cliff becomes fairly low, and is at 

 present untended in its upper portion, and consists of a steep slope of Boulder 

 Clay almost entirely obscured by grass. 



The Upper Boulder Clay is fairly constant in character, although collections 

 of erratics differ even when made in much the same locality. There seem 

 usually to be from 40 to 50 per cent, of Lake District volcanic rocks, from 

 40 to 60 per cent, of Silurian grits, from to 20 per cent, of Carboniferous 

 limestone, some Coal Measuie sandstones, and occasional Permian and other 

 Vocks. 



The following shells were recorded by De Ranee 1 as having been found 

 in the Blackpool district, the nomenclature having been brought up to date 2 . 

 Where the modern name differs from that given by De Ranee, the latter's is 

 placed in brackets after it. 



L = found in Lower Boulder Clay. 



M = found in Middle Sands and Gravel. 



U = found in Upper Boulder Clay. 



— M — Patella vulgata L. 



— M — Gibbula cineraria (L.). (Trochus cinerarius, Linn.) 



— M — Littorina littorea (L.). 



1 De Ranee, ' Superficial geology of .... south west Lancashire,' Mem. Ceol. Survey, 

 1877, p.p. 128-130. 



2 For revising this list in accordance with the arrangement and nomenclature as in Winckworth s 

 1932 list (Journ. Conch., vol. 19, pp. 217-252), I am indebted to Miss N. Fisher, of Liverpocl 

 Museum. 



