Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/127

Rh LATER TERTIARY GEOLOGY OF EAST ANGLIA. 89 with few exceptions are now concealed) then no doubt cropped out along the valley-sides. The degradation of these formed the chalky clay shown under the letter a in sections V. and VI. About Lyng and Elsing, however, the Chalk only comes out in the extreme bottom of the valley, while the Contorted Drift, having lost much of its brick-earth character, usually presents the appearance of a gritty bed with but little argillaceous matter and full of grains of chalk. The degradation of this, and, in a subordinate degree, of the chalk floor also, seems to have furnished the material of the bed a in this part of tho valley. The exposures of this bed along the Wensum valley about Lyng and Elsing all occur on the narrow strip of Chalk which crops out from beneath the Contorted Drift, and occupies the valley between it and the edge of the sheet of alluvium and Post- glacial gravel which skirts the river ; and they might be mistaken, by any one not possessed of an intimate acquaintance with the geological features of Norfolk, for the Contorted Drift itself ; but in the many sections of it which occur in the neighbourhood, that drift persistently maintains a different colour (tawny brown) and a less sandy composition. Tho Upper Glacial does not reach north of the line of section IX., in Central Norfolk, the country lying between the head of the Wen- sum valley and the sea being occupied exclusively by the Contorted Drift, overlain irregularly by the Middle Glacial. Near to the head of the Wensum valley a small stream takes its rise, and runs northwards to the sea through this Contorted-Drift area, its valley being excavated exclusively in that drift, which, in much greater thickness than near Norwich, is cut through down to the Chalk. The length of this valley is about ten miles ; and the following line of section (No. X.) taken about midway of its length shows its structure. Fig. 10. — Section X, across the Walsingham Valley. (Length 2 miles. Vertical scale 17| times the horizontal.) Railway- *; cutting at ~ Walsingham > Station. ps E. 10. Postglacial valley-gravel and recent alluvium. The country round this part abounds in sections of the Contorted Drift, which consists of a gritty white marl, a condition which it gradually assumes westward along the coast section ; so that from being a red brick-earth with included masses of marl in Central Norfolk, forming rich mixed soil, it gradually changes into this