198 Mr. 8S. V. Wood on the Red Crag 
clays. These variations occur within a radius of about a 
quarter of a mile from the London-Clay boring, showing that 
during the progress of the lower Drift the sea had eroded and 
encompassed an island of London Clay, by the sides of which it 
deposited its sands, but the top of which was never covered by 
that sea, but was overflowed when the great depression brought 
in the upper Drift. The lower Drift is cut through by the 
railway from London to Yarmouth, without any break, from the 
point where it is lost under the upper Drift near the Norfolk 
boundary of Suffolk to its termination at Chelmsford; and the 
railway-cuttings afford a continuous section, and show the sands 
that occupy the Crag-area and the country to the northward 
gradually changing into gravels as the more southern portions 
of the deposit are cut through. 
I have indicated on the small map the outcrop of this forma- 
tion from beneath the overlying Clay Drift along the eastern 
side of it; but the western outcrop I have not ventured to de- 
lineate, as it is some years since I visited the extensive develop- 
ment of the deposit around Brandon. The junction-line con- 
necting the western side of that development of the deposit with 
the emergence of the deposit from beneath the Clay at Writtle 
(and forming between those places the western boundary of the 
formation), being hidden by the overlying Clay Drift, is only to 
be ascertained accurately by the well-borings: these I have not 
yet been able to collect, but I have indicated on the map what 
may be taken as an approximation to that line. North and 
west of Brandon, the lower Drift has undergone a denudation 
along the fen-border; and I have not had the means yet of 
testing precisely where the boundary-line of the deposit, shown 
by the upper Drift resting on the Secondaries, as in Lincolnshire 
and Bedfordshire, without the occurrence between them of any 
lower Drift, is to be drawn. 
The thickness of the lower-Drift beds appears very uniform : 
the well-sinkings above Woodbridge give from 60 to 70 feet. 
Nearly the entire deposit is exposed at the scarp by Wilford 
Bridge over the Deben, near Woodbridge, the Crag occurring 
about 5 feet below the pit, and the upper or coarse gravel-beds 
remaining undenuded ; the thickness there is between 60 and 
70 feet. Danbury seems to show a greater thickness, but there 
perhaps something may be deducted on account of a slight 
bending of the beds over the hill. 
The transition from the lower to the upper or Clay Drift, 
although most abrupt, is unmarked by the slightest evidence of 
violence ; the sands and gravels give place to the clay sharply, 
passing, by a very thin band of loam, into each other. Sections 
showing the passage are not so common as might, from the 
