198 Mr. S. 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 



