126 M. M. Brydone — Further Notes on the Trimmingham Chalk. 



undonbtedly genuine cases, to be explained as above. But it is quite 

 possible that the majority are only apparent. If boulder-clay was 

 banked up against a vertical wall of chalk, the plane of junction 

 would often be a waterway of some importance. The water 

 percolating along this plane would, of course, have little or no effect 

 on the boulder-clay, but would tend to dissolve away the chalk, and 

 the deeper below the surface the water got the greater would be the 

 pressure on it and consequently its solvent power. There would thus 

 be a constant tendency for the chalk face to recede, and recede less 

 rapidly at the surface than deeper down, and so to develop an over- 

 hanging vertical face. The clay, being comparatively plastic, would 

 of course follow the receding chalk wall, and in time lie under the 

 chalk for a short distance. The shortness of this distance would 

 not be apparent in the foreshore sections we have, which are almost 

 always along the chalk walls and never across them, but I have 

 several times been able to satisfy myself by digging that the distance 

 for which the infraposition of the clay to the chalk extended seawards 

 was a matter of inches only. 



It may perhaps be permissible to speculate on the epoch at which 

 this chalk cliff existed. Now we know, of course, that the early Crag 

 sea was a warm and tranquil sea, and therefore it must have beeii 

 protected from the North Sea of the period by a land barrier, the 

 gradual breaching of which would allow the gradual admission of 

 colder water and Boreal forms, which can be so clearly ti'aced in the 

 upper Crag beds. Such a barrier, if it lay anywhere in or near 

 Norfolk, must have been of chalk, which is the basement bed, so to 

 speak, of the county, and we should therefore hope to find with great 

 luck the cliffs left by the cutting through of the barrier, and possibly 

 also the floor of chalk formed in the gap. Now we have between 

 Cromer and Weybourne an almost flat surface of chalk at sea-level, 

 which presumably has not been formed by the recent sea, as the 

 cutting back of the cliffs always reveals a platform of chalk at their 

 very base, which, except between Sheringham and Weybourne, shows 

 no sign of rising into the cliff, and therefore must be of pre-glacial 

 age. Is it fantastic to suggest that the chalk between Cromer and 

 Weybourne is part of the floor of the old breach, and that at 

 Trimmingham we have the only remains j'et disclosed of the east 

 cliffs formed by that breach, and that the west cliffs are buried at 

 some point between the chalk at sea-level round Cromer and the 

 chalk at a considerable height above it round Holt and Melton, 

 a slight tilt having brought the cliffs at Trimmingham nearly down 

 to modern sea-level ? The behaviour of the Pliocene beds themselves 

 confirms this supposition as to the relative Pliocene positions of the 

 Trimmingham and Cromer chalk, for the Pliocene beds near Cromer 

 are all above the surface of the chalk there, while we know on the 

 authority of Mr. Reid that corresponding Pliocene beds at 

 Trimmingham close by the chalk occur well below high tide mark, 

 and consequently many feet heloio the highest point to which the 

 undisturbed chalk there reaches in the south bluff. This theory 

 would involve the existence at one time of a (probably now buried) 



