1 92 W. H. PEXNTNG ON THE PHYSICAL GEOLOGY OP 



forming an escarpment roughly parallel to that of the Chalk. The 

 northern and eastern portions of the district are in part occupied 

 by deposits of later Tertiary age — the Crags, the ChiLLesford beds, 

 and the Forest-beds. 



The general altitude of the line of escarpment of the Upper Chalk 

 may be taken as from 300 to 500 feet, that of the London Clay 

 from 200 to 300 feet above the sea. 



Paet 1. — The Drift-deposits to the South and East of the Chalk 

 escarpment. 



Pliocene. — Along the coast of Norfolk, Suffolk, and part of Essex, 

 as well as for some distance inland, occur the " Crag" deposits. Of 

 these sands, the older or " Coralline Crag " contains the remains of 

 a deep-sea fauna ; in the " Red Crag," immediately succeeding, 

 littoral forms prevail; while the newer or "Norwich Crag" also 

 contains littoral forms with land and freshwater shells in addition. 

 A gradual rising of the coast during the Crag period is thus indi- 

 cated ; and this continued until the land stood slightly higher than 

 at present, admitting the growth of the Cromer " Forest-bed." 



These Crag-beds perhaps scarcely belong to the drift-deposits that 

 present the evidence on which the following arguments are founded, 

 although I believe that there is a gradual passage up from them to 

 those of recent date. This gradual passage will probably be found 

 to exist stratigraphically, as well as in regard to their enclosed fos- 

 sil remains and to the climate * that prevailed during the different 

 periods of their deposition. 



Lower Glacial. — After the formation of the Cromer Forest-bed 

 the land again sank beneath the water, gradually and to a depth 

 of certainly not less than 400 or '500 feet f : during the progress of 

 the submergence the advancing shore-line gave rise to the "pebbly 

 sands" which, according to Messrs. Wood and Harmer, "form the 

 base of the whole glacial series, indicate shore-conditions and the first 

 setting-in of the great glacial subsidence " %. Arctic conditions of 

 climate began to prevail ; and here and there patches of clay were 

 dropped by icebergs, heralds of those to follow in such vast numbers 

 during the Upper Glacial epoch. The contorted drift, which occupies 

 a large area in the north-east portion of the district, was deposited 

 during the early part of this submergence of the land ; its mode of 

 formation I consider to have been much the same as that of the 

 Upper Boulder- clay presently to be considered. The contortions 

 sometimes exhibited by this deposit are probably due to agencies 

 acting on the clay at a subsequent period. 



Middle Glacial. — The Lower Glacial beds are overlain and con- 

 siderably overlapped by a series of gravels and sands called the 

 " Middle Glacial." These beds occupy, or have occupied, almost all 

 the area covered by the Lower Glacial, and extend far beyond it in a 

 southerly direction. It will be seen on reference to the map (fig. 1, 



* Lyell, ' Student's Elements,' p. 177. 

 t Lyell, ' Student's Elements,' p. 167- 



of the Upper Tertiavies of East Anglia,' p. 16. 



