VI. Outlines of the Geology of Cambridgeshire. 



By the Rev. J. Hailstone, F.R. & L.S. Woodvvardian Professor in 

 the University of Cambridge. 



Read November 18th, 1814. 



T, 



HE upland parts of Cambridgeshire consist of chalk hills, 

 being part of that great range which traverses the island in a south- 

 easterly direction, from Dorsetshire to the Yorkshire coast. At 

 their northern extremity they appear to rest upon an extensive 

 bed of blue clay, provincially called gault. They are composed 

 of both the varieties of chalk ; of the upper containing the com- 

 mon black flint in abundance ; and the lower or grey chalk, which 

 contains little or none. If a line be drawn from Royston by 

 Balsham to Newmarket, it will pretty exactly define the limits of 

 both the varieties ; the hills to the eastward being composed of the 

 upper beds, while those to the west consist of the lower or grey 

 chalk. Further to the east, on the borders of Suffolk and also of 

 Essex, the chalk disappears under a thick bed of clay, which 

 occasions a corresponding difference in the soil and its produce. 

 To the west, a succession of hills composed of beds of grey chalk 

 with wide intervening vallies of gault occur ; till on the extremity 

 of the county, at Gamlingay and Potton, a tract of sand comes in, 

 evidently connecting the strata of Cambridgeshire with those of 

 Bedfordshire. And here the features of the former county undergo 



2h 2 



