Inverted Mass of Upper Cretaceous Strata. 107 



a, floor of Devonian sandstone. This compares closely with the 

 mode of occurrence of the similar lenticles at Shenley Hill and adds 

 strength to our inference that we have here a basement-bed of the 

 varians Chalk, laid down during the period of early Cenomanian 

 movement and transgression. No later deposit of Cretaceous age 

 is preserved at Shenley Hill. 



The above brief description of events during Cretaceous time 

 explains much confusion in the account of the strata ofiered by 

 Messrs. Lamplugh & Walker. The brachiopod-bed (D) of those 

 authors was ascribed by them to the Lower Greensand. In reality 

 it consists of rock-masses belonging to the basal bed of the Chalk 

 and the basal bed of the Upper Gault. The idea of a " peculiar " 

 faunal assemblage, founded on a collection of specimens obtained 

 from the rocks of both zones, was bound to be erroneous, particularly 

 in view of the fact that some Lower Cretaceous species were found 

 which were not indigenous to either of these horizons. Mr. Walker's 

 recognition of so many links with the Tourtia-faunas of the 

 Continent, whichever local " Tourtia " it might be, now gains a new 

 significance. Transgressive basement-beds formed under conditions 

 of active erosion are likely to contain species derived from any 

 fossiliferous stratum of earlier age exposed to denudation at the time. 



B. Events during and since Glacial Time. 



It is evident that before the advance of the ice-sheet the Upper 

 Gault in the neighbourhood of Shenley Hill was capped in places 

 by the remnants of the Upper Greensand, with the lenticles of basal 

 Cenomanian age extending over both. It is impossible to say 

 whether any of the Chalk Marl here had still survived the ordinary 

 processes of subaerial denudation. So far as the overturned mass 

 of strata is concerned, no Chalk Marl was jDresent. 



The inversion of the sheet of strata now seen in an abnormal order 

 of succession at Harris's Pit must be regarded as an effect of the 

 glaciation of the district. The elevation of the ground probably 

 opposed an obstacle to the advancing ice-sheet,^ with the result that 

 a huge mass of rostratus Gault and its thin capping of later strata 

 became detached, carried forwards towards the south or south-east 

 and completely overturned upon a floor formed, on the lower ground, 

 by the basal joart of the Upper Gault. It seems improbable that such 

 a large mass could have been transported far from its original site. 



It is remarkable that there are so few signs of disturbance at the 

 present base of the inverted beds ; and although there is sufficient 

 •evidence of squeezing, disruption, and confusion in the present 

 state of the topmost bed of the substrata, this is only such as might 

 result from simiDle crushing, without any continued forward move- 

 ment of the transported mass after it reached its new resting-place. 



' Compare remarks by H. B. Woodward, " The Chalky Boulder-clay and 

 the Glacial Phenomena of the Western Midland Counties of England " : Geol. 

 Mag., 1897, pp. 495-6. 



