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 



* Cromer Lighthouse-hill is given in the Book of Levels published by the 

 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. 



