﻿20 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 20, 



I prepared in the beginning of 1847, for the Memoirs of the Geolo- 

 gical Survey of the United Kingdom ; in which the erratic tertia- 

 ries of Norfolk were compared with a small portion of those of South 

 Wales, which I had mapped, during part of the preceding summer, 

 for the Government Geological Survey. As various unexpected cir- 

 cumstances have delayed the publication of that paper, and as I un- 

 derstand there is no prospect of its appearing at present, I am de- 

 sirous of now placing on record its principal generalizations so far as 

 regards my work in Norfolk, before I joined the Geological Survey, 

 referring to that memoir, when published, for details. 

 Those generalizations are — 



1 . That our views of the glacial or erratic period are very incom- 

 plete if we consider its deposits merely as a formation, which lay for 

 ages beneath a sea, through which icebergs, straying from northern 

 regions at the same annual average rate as at present, dropped their 

 loads of foreign detritus, here and there, until the floor of the ocean 

 became thickly strewn with boulders, as seen in the regions of Europe 

 and America now covered by the erratic tertiaries or northern drift. 

 Such views are incomplete, because our own island affords the means 

 of fixing the precise point from which the commencement of the 

 glacial period dates, and of proving that Britain sank as well as rose 

 during that period. These proofs consist in the forest of Happis- 

 burgh and Cromer buried beneath the erratic tertiaries, as first de- 

 scribed by Taylor and Woodward ; and in the circumstance that on 

 the western coast the northern drift, with its marine remains, has 

 penetrated into Cefn Cave, and, by its superposition to the deposits 

 containing mammalian remains, testifies, like the buried forest, to the 

 presence of a subaerial surface immediately before the transport of 

 northern blocks. 



2. The date of this subaerial surface was subsequent to that of the 

 mammalian crag, on which are rooted the buried trees of Happis- 

 burgh and Cromer ; and whatever indications the faunae and florae of 

 the red and mammalian crags may afford of an approach to an arctic 

 climate, the true glacial phaenomena of transported blocks do not 

 commence, in Britain at least, until during the submergence of the 

 desiccated and tree-bearing surface of the latter. 



At the commencement of that submergence, a bed of marine shells 

 at Runton, in situ, above the fluvio-marine deposit on which the 

 forest stands, testifies to marine conditions not very dissimilar from 

 those of the crag, quickly succeeded by the peculiar phaenomena of 

 the till or boulder clay, with its broken shells, erratic boulders, 

 scratched and subangular detritus, and masses of fragmentary chalk, 

 unabraded and unmixed with other matter, in a manner very difficult 

 of explanation, if the transport were not effected by means of some 

 buoyant material. At Mundesley the early part of the submergence 

 is marked by the interlacing of peaty mud and freshwater shells with 

 the till, as described by Sir Charles Lyell *, and attributed by him to 

 the entry of a river into the sea at that point. 



3. The erratic deposits form continuous sheets of strata, more ex- 



* London and Edinburgh Phil. Mag. 1840, vol. xvi. p. 353. 



