LOWER CHALK—CONDITIONS OF DEPOSITION. 
347 
however, have been found by Mr. H. Woods in the coprolite bed 
at the base of the Upper Gault at Stanbridge, near Leighton 
Buzzard (see p. 196). Similar large blocks have been found in the 
Chalk Marl of Bur well, in Cambridgeshire, and at Gay ton, in 
Norfolk.* While, therefore, some of the rock-fragments in the 
Cambridge Greensand may have been derived from the Gault, it 
seems probable that most of them were dropped on the sea floor 
during the formation of that deposit. 
When they were first described j it was suggested that ice was 
the means of transport and it is certainly difficult to understand 
by what other means the larger blocks could have been carried, 
though those of smaller size might well have been transported by 
the agency of trees swept down by rivers in times of flood. 
It is, of course, possible that there was a cold current from the 
north or north-east which met a warm current from the south¬ 
east, much as the Labrador current meets the Gulf Stream current 
at the present time, and that the stones were dropped by the melt¬ 
ing of ice floes. It is also possible that these floes came from the 
coast of a vanished land which then united Scotland with Norway, 
and this would account for the likeness many of the fragments 
bear to Scotch and Norwegian rocks. If they had been brought 
by a current from the north-west we should expect that many 
of them would be traceable to existing north-western sources, 
which is not the case. 
There remains Mr. Whitaker’s suggestion that the transported 
fragments came from the eastern land, but until we know more 
of the rocks which formed this land it must remain only a sugges¬ 
tion. If such were their source we cannot call in the agency of 
icebergs, but river-ice such as is formed in the St. Lawrence at 
the present time and occasionally even in the Thames would be 
capable of transporting the blocks above mentioned. Even this, 
however, would indicate a colder climate than we generally 
associate with the Cretaceous period, but in this connection it is 
noticeable that coniferous wood is common in the Gault and 
Upper Greensand. 
As mentioned on p. 344, there are proofs that another strong 
current flowed across Devon and Dorset, and there is good evi¬ 
dence of its having been strongest in the far western localities, 
its velocity diminishing in an easterly direction, though its influ¬ 
ence is still visible in the Isle of Wight. Even at Cap la Heve, in 
Normandy, proofs of current action are very apparent in the bed 
which we regard as the eqfuivalent of our Chloritic Marl. 
So powerful was the action of these currents that for a time it 
was only in a comparatively small area that sediment was permitted 
to accumulate. The earliest Cenomanian sediments in Britain 
were the beds composing the sub-zones of Catopygus columbarius 
* See Quart. Journ. Geol. Soc., Vol. xliii. p. 554, and Mem. Geol. Survey 
Expl. of Sh. 65, p. 35. 
t Quart. Journ. Geol. Soc., Vol. xxix. p. 11. 
