100 ' PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [ Dee. 8, 
débris that makes up so large a part of the chalky Boulder-clay, it 
will, I think, be apparent that had there been either a sea or a dry 
valley unoccupied by ice to receive it, the chalk débris, so far from 
being entirely absent in the clay would have been extremely abun- 
dant. None but those who have spent years in the examination of 
it over the greater part of the east of England can form an idea of 
the enormous volume of the chalk contained in the great Boulder- 
clay of the south-east. The proportion of this material may be 
estimated at from 10 to 90 per cent in different localities, the pro- 
portion being usually greatest in the counties of Norfolk, Suffolk, 
Essex, Hertford, and Lincoln—in the latter county, for a great dis- 
tance along the western flank of the Wold, the clay being so nearly 
chalk itself as to be quarried for lime; and the quantity is still 
considerable in other counties, such as Huntingdon, Cambridge, 
Rutland, Leicester, Northampton, Warwick, Bedford, and Bucking- 
ham. Most of this chalk débris consists of lumps of rocky chalk 
of various sizes, unlike the soft material of which the upper Cre- 
taceous formation of the south is principally composed, and so hard 
as to require a hammer to break it*. In these characters it is 
identical with the chalk of the Yorkshire Wold, which is all of this 
hard kind; and in it I have found, in sections where this chalky 
clay overlies the middle Glacial sands, rolled lumps of the red 
ehalk which forms the base of the northern chalk, but is absent 
from the southern. The highest position at which the red chalk 
erops out in England is more than 300 feet below the higher eleva- 
tions to which the chalky clay attains, and which were therefore 
under the sea when the red-chalk lumps, coming from a much 
lower level, were imbedded in its deposit. 
If we consider the soluble nature of chalk, it must, as it seems to 
me, be evident that none of this débris can have been detached 
from the parent mass either by water-action or by any other atmo- 
spheric agency than moving ice. 
The action of the sea, of rivers, or of the atmosphere upon chalk 
would take the form of dissolution, the degraded chalk being taken 
up in minute quantities by the water, and held in suspension by it, 
and in that form carried away; so that it seems obvious that this 
great volume of rolled chalk can have been produced in no other way 
than by the agency of moving ice; and for that agency to have operated 
to an extent adequate to produce the quantity contained in the great 
chalky clay before its denudation (a quantity that I estimate as ex- 
ceeding a layer 200 feet thick over the entire Wold) nothing less 
than the complete envelopment of a large part of the Wold by ice for 
a long period would suffice. Nor, as it seems to me, can we explain 
the detachment of lumps of the red chalk from the outcrop of the 
parent stratum, far below the level reached by the sea that de- 
* Quite different is the chalk in the Lower Glacial of Norfolk. The marl 
into which the contorted drift passes, and of which great masses are also im- 
bedded in the coast, or silty development of that deposit, is a soft greasy accu- 
mulation, formed out of the soft chalk of the cretaceous districts south of the 
Wold. 
