TRIMMER ON SAND-GALLS IN THE NORFOLK CHALK. 



315 



very little attrition ; and sometimes this constitutes almost the 

 sole material ; sometimes there is an admixture of a variable 

 proportion of sand and clay. The lower deposit, though very 

 generally distributed, is more local than the upper. There can 

 be no doubt that both belong to the northern drift. 



The surface of the lower deposit is often very much eroded with 

 conical and cylindrical pipes, and with irregular furrows from a 

 few inches to a foot or two in width, and rarely more than 3 or 

 4 feet in depth. I gave in the same paper an instance of this 

 at Gallows Hill, near Burnham Market, on the side of a valley 

 which opens to the sea, and is excavated in the solid chalk. This 



Fig. 14. Burnham Market. 



Y 10 feet. 



' 20 feet. 



9- 

 h. 



Ferruginous sand, with unabraded flints, and pebbles of trap and porphyry. 

 Lighter-coloured gravel, with angular flints, rounded pebbles of chalk, and 



pebbles of trap and porphyry. 

 Where the lining is darker, is a lining of clay. This lining extends also 



round the sand-pipe p. 

 Comminuted chalk, mixed with clay and sand, and with rounded and par- 

 tially waterworn fragments of chalk. 

 Large tabular unabraded masses of flint. 

 A bed of gravel. 

 Solid chalk. 



mass (r, r) was 20 feet thick, and consisted of finely-comminuted 

 chalk detritus, mingled with clay and sand, and containing rounded 

 and slightly waterworn fragments of chalk, and large tabular 

 flints, not in the least abraded. It had seams of sand, several 

 inches thick, in its lower part ; and one of these expanded into a 

 bed of gravel 2 feet thick. It was traversed by a sand-pipe (p), 

 which appeared to extend through its entire thickness. 



In a recent communication I mentioned a bed of chalk-rubble 

 near Trimmingham, which occurs enveloped in drift, and is so 

 pure as to be burned for lime. I have since met with another 

 such deposit near the Thorpe entrance to Gunton Park, which is 

 also burned for lime : it consist of fragments of chalk which have 

 undergone some little attrition. This bed is from 12 to 15 feet 

 thick ; rests upon sand ; and is covered by from 2 to 4 feet of 



