﻿Quart. Journ. Geol, Soc. Vol, LXIV, PI. XXXYII. 



I 400 to 600 feet thus.- 



Mai' oy THE Alton Distuiot. 



[Tlic courses oi' tbe principal valleys are marked by rlotfed linet,. The heavy bi-okeu line marks 

 approximately the lower outline of the Chalk. "j 



