Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/117

Rh LATER TERTIARY GEOLOGY OF EAST ANGLIA. 79 valleys occur. The surface of this floor is a few feet above high- water mark at the western extremity of the coast section at Wey bourn, from whence it descends very gradually in a space of 8 miles to low-water mark at Cromer, rising again gradually to the beach-level about Trimmingham, where for a very short distance it- is bent up into an arched boss, some 15 feet above the beach, and from which place it sinks gradually eastward and becomes lost under the beach. From the point where it thus disappears its place is taken by beds of the Preglacial-forest age as far as Hasboro' ; so that we thus are enabled to trace the Preglacial floor for a distance of nearly 20 miles, and perceive that it is entirely unconnected with the valleys which indent the surface of the country thus intersected. These valleys are several in number, the deepest being that in which Cromer stands, and which, measured from the top of the Lighthouse Hill, has a depth of more than 200 feet*. So far also from this valley having an)^ connexion with the slight depression in the Chalk floor towards Cromer to which we have referred, this hill occupies the centre of that depression. The valleys thus intersected are seen by the cliff-section to be cut out of the Cromer Till and overlying Contorted Drift, which, with the pebbly sands underlying and interbedded with the base of the Cromer Till, form what we have termed the Lower Glacial series — a formation which, as proved by the height attained by some of its least-denuded por- tions, must before denudation have had a total thickness of nearly 250 feet in this part of Norfolk. Covering this formation in a more or less intermittent way, and resting always on a deeply marked denuded surface, occurs the sand and gravel which we have referred to Middle Glacial age. This sand and gravel along the cliff-section occupies troughs excavated in the Lower Glacial deposit below it in those parts where it extends continuously ; but in places it also caps hills formed of the Contorted Drift, though not in an even way ; that is to say, it hangs on one side or other of the prominence of Contorted Drift, showing that it once occupied a trough, the central part of which, having been further denuded Postglaciallv, does not now retain any of the sand and gravel in it. As we have in the sections annexed to the map which accom- panies our " Introduction " given one in great detail of this cliff, we refer to it in lieu of offering a representation here. This long natural section thus shows us that the valleys are in- dependent of the Preglacial floor upon which the Glacial beds rest, and that these valleys had their commencement in a denudation which intervened between the uppermost of the Lower Glacial series, the Contorted Drift, and the deposition of the Middle Glacial sand and gravel ; and it seems to us that all the evidence afforded by Ordnance department as 248 feet above Ordnance datum, and there are still higher elevations in the neighbourhood. A small part of this elevation is made up of the Middle Glacial sand ; but as this always lies more or less in a slanting position, very little deduction need be made for it.
 * Cromer Lighthouse-hill is given in the Book of Levels published by the