﻿486 S. V. Woocl,jun. — Ainerican and British 8urf ace- Geology. 



clay was converted into land and denuded, and then subsequently 

 depressed beneath the sea ; but this view was only offered by us 

 as an hypothesis alternative to that which we regarded, and which 

 I still regard, as the true one, viz. a change in the source of the 

 morainic material due to the recession of the ice from the chalk 

 country, which the gradual diminution upwards in the overlying 

 clay of the chalk debris, and its eventual disappearance in the 

 uppermost portion, seemed to us to indicate. In many sub- 

 sequent references that I have made to the purple clay of York- 

 shire, I have invariably regarded it as one continuous deposit 

 with the chalky clay of East Anglia, and with the chalky clay 

 which, underlying the purple, forms the base of the Grlacial forma- 

 tion of South-Eastern Holderness, and seems identical with that of 

 East Anglia. So far from being a separate deposit, this purple clay 

 with lessening chalk debris, forms, in my view, about the middle 

 portion of that one unbroken formation, the Upper Glacial, the 

 deposit of which took place mainly in the horizontal form, and of 

 which the chalky clay of East Anglia, and that forming the base- 

 ment clay of South-East Holderness, constitutes the earliest and 

 preceding part, and the chalkless clay of Holderness, into which 

 the purple clay with chalk passes up, and the clay of the more 

 northern counties, constitutes the succeeding parts. 



Ee verting to the case of morainic clay resting upon stratified 

 sands with marine shells, I would call attention to the evidences 

 which are available to show what kind of effect has actually resulted 

 from the action of glacier-ice upon strata softer than rock when 

 these formed the floor occupied by it. Thus in Norfolk we have 

 evidence of glaciers having occupied the valleys which were cut out 

 of the Lower Glacial and Crag beds down to the Chalk, and left 

 their moraine upon that formation as they receded.^ Where this 

 has occurred, not only is the Chalk beneath the moraine matter 

 altogether altered in character, having become a greasy marl, but the 

 lines of flint which it contains are ruptured, and forced violently 

 upwards, and crumpled together. This feature is most conspicuous 

 nearest the surface where the grinding pressure of the glacier on its 

 bed was most felt, and becomes less and less downwards until deep 

 down (in some cases not until a depth of twenty feet in this solid, 

 though altered. Chalk is reached) the lines of flint are found to 

 regain their undisturbed state. A representation of this action of 

 glacier-ice upon the Chalk at Litcham was given by me in 1866, 

 in a paper in the Quart. Journ. of the Geol. Soc. ; '^ and in a 

 subsequent part of the present paper also I shall have occasion to 

 describe the action of an ice plough on sands in the Yare Valley, 



1 See paper by myself and Mr. Harmer on the later Tertiary Geology of East 

 Anglia, in Quart. Journ. Geol. Soc. vol. xxxiii. p. 74. 



^ vol. xxiii. p. 84. Instead of this action on the Litcham chalk having (as re- 

 presented in the paper quoted) taken place during the formation of the Contorted 

 Drift, I should now refer it to the time when, after the elevation of part of the 

 Upper Glacial into land, the inland-ice pressed on the west of Norfolk, as explained 

 in the sequel of the present paper; the bed b of the section in the paper quoted not 

 being, apparently, the Contorted Drift. 



