36 ON SOME ANCIENT LAKE REMAINS AT FELSTEAD, WITH 



course. This gravel furnishes oyster-shells, and a fragment of pottery 

 has been found in it. Beyond the transverse section made by the 

 present channel, we are in complete ignorance of the further course 

 of this bed, as it is buried under some feet of later deposits. This 

 gravel, from the compactness and narrowness of its bed, seems to be a 

 product of slow erosion, and must have been obtained from the deep- 

 ening rather than the widening of the channel of overflow. It may 

 have been that the wear of the stream took off the coating of Clay 

 and choked-gravel and exposed porous sands and gravel, which are 

 known to exist near by, and so drained the lake to an inconvenient 

 extent. Whatever may have been the cause, the dam was after- 

 wards made good at that end and the overflow was transferred to the 

 other end of the dam. After this alteration the gravel and shelly- 

 marl that we have mentioned, received no other addition but that 

 due to the wear and tear of the seasons. A coating of rainwash 

 derived from the Boulder Clay and Glacial gravel of the valley side 

 was slowly deposited, and entombed the ashes of the fire, the shell- 

 marl, and the gravel with oyster-shells. This rainwash ultimately 

 attained a thickness of eight feet ; but it has received no addition for 

 a great number of years, as we shall show further on. 



Turning now to the inside of the lake, we note that at some 

 time in its history, which does not appear to be at the beginning, a 

 considerable quantity of Chalky Boulder Clay was thrown into its bed. 

 This clay now exists with the lumps of chalk intact, and rests at one 

 place on lake mud with oyster-shells, and is itself overlaid by two 

 feet of lake mud, also with oyster-shells and a fragment of Roman 

 pottery, showing clearly that after its deposition the lake still existed 

 and was used by the inhabitants as in days gone by. The confusion 

 of deposits at different parts of the lake's bed is very great. The 

 bed seems to have consisted of gravel overlaid by peat at the time 

 the dam was made. In one place we now have :— 



Rainwash ........ 



Lake Mud — very compact — (one piece of Roman 

 pottery found here) ...... 



Chalky Boulder Clay 



Peat 



Gravel (not bottomed) ...... 



Feet. 



