14 . INTRODUCTION. 



limestone of Durham and Yorkshire ; the new red sandstone 

 of Lancashire, Cheshire, and the Western Midlands ; the 

 oolitic limestones and clays of the northern and central plains ; 

 the pink granite, gneiss, and quartzite of the Highlands ; the 

 basalt of the heights of mid-Scotland, and perhaps of north- 

 east Ireland ; and the greenstone, greywacke, pink syenite, 

 felstone, chert, porphyrite, Lydian stone, and porcellanite of 

 the lower Silurian beds of south Scotland and Cumberland. 

 These fragments seem to imply the existence of a large ice- 

 stream passing from the region of the Grampians in a south- 

 easterly direction over the Yorkshire wolds to the coasts of 

 Norfolk and Suffolk, where, coming in contact with the more 

 powerful ice-sheet of the German Ocean, it was compelled to 

 diverge to the south-west until it melted in the valley of the 

 Thames.* 



The Glacial series is divided into three principal beds. 



No. 5. Lower Drift. This is also known as the Lower 

 Boulder Clay. It is often difficult to separate from the suc- 

 ceeding Middle Drift, but it may be seen at the bottom in the 

 Wey bread Brickyard, and perhaps in a recently-opened pit at 

 the foot of Needham Hill. Its contorted character was well 

 shown formerly in a pit at Starston, near the Rectory, t Sec- 

 tions are exposed in pits near Denton Church ; and on the 

 Bath Hills the three beds of the series are distinctly traceable. 

 The Lower Drift generally consists of a brown sandy loam, 

 with erratic stones and but little chalk. It is particularly 

 serviceable for brick-making. 



No. 4. Middle Drift. This is generally exposed on the 

 sides of the valleys of the Waveney and its tributaries, where 

 it is not overlaid by the river gravels. A good section of its 

 fine sands is visible in the pit at Mendham on the Withersdale 

 Road, and in the large pit on Shotford Heath, where they may 

 be seen covered immediately by Post-Glacial gravel. The 

 Middle Drift was probably deposited in very shallow water, 

 subject to strong currents, and under a climate milder than 

 that of the Lower and Upper Periods, which caused the 

 glaciers to retreat for a, time. It is almost entirely destitute 

 of organic remains, and its chief economic value is the water 

 supply of the district .J 



* Geikie, The Great Ice Aye, ch. xxix. 



f Geological Magazine (1868), p. 454. 



X "The junction at Potter's Pits, Weybread, between this formation and a 

 loamy clay below is most interesting. The water filters through the sand 

 till it reaches the underlying and impervious bed, at which point it trickles 

 out on the face of the section. A vigorous growth of coltsfoot ( Tussilayo 

 Farfara), which is cut off in a clear line at the top of the clay where it 

 meets the sand, shows the junction even where the slope is completely 

 grassed." C. C. 



