PLIOCENE PERIOD Hf EN&LAirD. 485 



Now, if we bear in mind that during Stage II. the submergence of 

 the region to the north and west of the Crag estuary, which had 

 been land during the accumulation of the Crag beds, took place, and 

 that the sea-bed thus formed lay directly in the new path which 

 the ice took in consequence of the change of inclination, viz. 

 along the west of the Wold and towards Sheet 67, in which these 

 remains for the most part occur, it is easy to see that such remains 

 are those of MoUusca which lived during Stage IT., and during so 

 much of the present stage as elapsed previous to their removal ; and 

 may not therefore be altogether synchronous with each other, 

 though all of Glacial age, being the remains accumulated on the 

 sea-bottom in some locality favourable for their existence during 

 this time, which the ice in its advance ploughed out and sent on their 

 travels. Thus it is that this shelly band, like the debris of the clay 

 itself, occurs only within some three or four feet of the junction of 

 the sand and gravel g with the Chalky Clay. It is generally also 

 immediately beneath or associated with a vein of chalky gravel. 



We now come to the question as to how the Chalky Clay, 

 assuming it, as I do, to be the moraine of the land-ice, was deposited 

 or accumulated over this sand and gravel. 



Within the broken line shown on Map 1 (PL XXI.), the clay, 

 as a rule, rests on the Mesozoic formations, without the intervention of 

 a bed of sand or gravel, though sporadic occurrences of such a bed 

 are to be found ; but I have never met with any instance there 

 where this affords an example of the junction of the gravel or sand 

 with the clay of the kind shown in figs. X. to XIII. On the other 

 hand, the rare instances with which I have met present features 

 resembling the jagged termination of the clay in fig. XVIII., where 

 sand has been forced up into the clay. One striking instance of 

 this kind I found displayed at the base of Graffham-Wood cutting, 

 five miles W.S.W. of Huntingdon, in Sheet 52, when the railway 

 from Huntingdon to Thrapston was in progress of construction, 

 where, besides the surface of the sand being jagged into the clay, a 

 portion had been detached and imbedded in the clay. Over this 

 area also the Mesozoic floor on which the clay rests, where it con- 

 sists of rock, is frequently disturbed, grooved, or twisted. Where 

 the clay rests on the Chalk, that material is sometimes so altered as 

 to form a greasy water-holding marl, and often to graduate almost 

 into the chalkiest form of the clay itself. This greasy chalk prevails 

 near the Great Eastern Railway about Harling station, where the 

 Map is shown as uncovered by the clay, in the south-west corner 

 of Sheet QQ. In other parts within the broken line the chalk is 

 disturbed, and the lines of flint dragged up and displaced to a great 

 depth, as in the case of a chalk-quarry at Litcham, described by me 

 in the * Quarterly Journal' for 1866, p. 84*. This is immediately 

 west of that line in the N.W. of Sheet m. 



* In this paper I erroneously attributed the ice-action, thus dragging up the 

 chalk, to the Lower Grlacial period. The bed of chalky loam which I there 

 showed as underlying the Chalky Clay may, perhaps, not do so, but be, as the 

 gravel shown there under the letter d is, a bed due to the ice melting. 



