Seeley— On the Cretaceous Beds at Ely. 533 
Cretaceous beds are merely obscured by Boulder-clay let down in 
front of them, so that the fault may be much less than it appears to 
be. It is the same downthrow fault which lets down the Boulder- 
clay in front of the Shanklin Sands (Fig. 1). Another fault lets 
down Boulder-clay under the Chalk. 
The Boulder-clay (Fig. 1, 6) forming the greater part of the sec- 
tion is a drab-coloured clay, full of all sorts of rocks: it reaches from 
the bottom to the top of the pit, some forty feet. There are boulders 
of Mountain Limestone two or three feet in diameter, smaller pieces 
of Lias, and nearly all the Oolites ; Greensand Fossils, and masses of 
Chalk in plenty. At one place in the section the upper part is de- 
void of pebbles and boulders, and at the north end there are rough 
courses of nodules making a kind of curved stratification. The only 
contemporary fossils that Ihave found in it are some very old and 
thick specimens of Tellina. The junction with the Kimmeridge 
Clay at the north end is not clear, but it is almost certain that the 
Kimmeridge Clay extends in front of it. 
This faulted condition of the Drift, which stands quite perpendi- 
cular, side by side, with the older beds, is of peculiar interest as in- 
dicating its age to be probably anterior to the present form of the 
country, for all trace of the Boulder-clay is removed from the sur- 
face round about. 
This clay is capped with about fifteen feet of gravel, which is in- 
teresting as being in part interstratified with the Boulder-clay. 
This section (Fig. 1), so singular in the thinning off of all the 
Cretaceous strata, offers a few points for consideration. 
The Shanklin Sands, which in Bedfordshire are very thick, gra- 
dually thin off in a wedge to a few feet. There they rest on Oxford 
Clay, here on Kimmeridge Clay. The Gault thins off similarly in 
the same direction. The Greensand is constant, and the Chalk 
shows no sign of change. 
The wedge-like form of Shanklin Sands may result from the ma- 
terial of which it was built up having become less abundant to the 
north-east, and so the representation of as much time is compressed 
into four or five feet as is elsewhere represented by several hundred 
feet. The small pebble character of the bed does not indicate that 
it was accumulated far out at sea, where currents had no longer 
power to bear its material. And had it been formed near the source 
whence derived, where a shallow sea prevented a thick formation, 
the component particles, which are rarely more than half an inch in 
diameter, would have been larger ; and the absence of fossils is note- 
worthy. Hence, as it is so thin, and so like ordinary and far thicker 
sections, it seems almost certain that the deposit only represents a 
part of the formation. That part does not appear to be the newest, 
tor if it did, as there are no breaks in nature, it would pass up in- 
sensibly into the Gault, whereas there is an intermediate thickness 
in which the beds irregularly alternate ; which indicates not a gra- 
dual but a sudden change, such as depression of what had been land. 
Therefore the Gault appears to be unconformable to the Shanklin 
Sands. 
