244 Professor Hailstone on the 



a manifest alteration, its high elevations subsiding by degrees into 

 the sand hills of the latter. 



Upon some of the highest hills near Cambridge, a deposit of 

 gravel and loose stones in horizontal layers, has lately been found, 

 resting immediately upon the chalk. This gravel differs in so 

 many respects from the red ferruginous gravel found dispersed in 

 patches over the gault in the subjacent flat, that I think it must be 

 considered as a deposit of a different epoch. It contains numerous 

 fragments of strata belonging to the oolite series, which occur in 

 the neighbouring counties of Northampton and Rutland, surround- 

 ing Cambridge on the west and north-west. Pieces of basaltic 

 rocks are sometimes found, but these are not very common. These 

 fragments are of all sizes, and worn down in different degrees. 

 Some are pebbles intirely rounded ; others have their edges merely 

 blunted. Some appear so tender and so little capable of resistance, 

 that it is difficult to conceive how they have been transported 

 without being entirely destroyed. The prevailing material of these 

 masses of gravel, is the pale blue or light grey variety of flint, 

 with numerous traces of the alcyonium or other similar bodies in 

 its substance. 



According to my observation, this variety of chalk flint is not so 

 common In the southern parts of this great chain, whilst in its 

 continuation through Lincolnshire and Yorkshire, scarce any other 

 Is to be met with. The two principal deposits of the gravel of 

 which I have been speaking are to be seen on the summit of 

 Gogmagog hills, and on Harston hill about five miles to the south 

 of the former. The height of these hills may be estimated at 800 

 feet above the river at Cambridge. 



Harston hill has been examined by Mr. Warburton, Secretary of 

 the Geological Society, who has obligingly communicated the 



