Dr. FiTTON on the Strata below the Chalk. 305 



These accumulations, it will be perceived, closely resemble those already 

 mentioned in the account of Buckinghamshire and Bedfordshire, especially 

 near Leighton, and at Stevvkley. They occupy, in fact, a great extent of the 

 surface, and form one of the most interesting geological deposits throughout 

 the East of England ; but there are circumstances respecting their relations 

 to each other, and to the crag of Norfolk and Suffolk, which still remain to 

 be investigated and explained. 



(158.) The strata therefore which are found below the chalk in Cambridge- 

 shire, consist of Chalk, Upper green-sand, Gault, Lower green-sand, Kim- 

 meridge clay, Oxford oolite, and Oxford clay ; the last occurring only in a few 

 places, and in the remote part of the county, in which it is the lowest member 

 of the series. The sections, Plate X. a, Nos. 22, 23, and 24, explain the 

 general relations of these strata, but have no pretensions to accuracy of local 

 detail. The following notes describe some of the principal appearances con- 

 nected with the object of this paper; and the publication of the Ordnance 

 maps of the county will no doubt soon lead to the complete examination of 

 it by the geologists of Cambridge. 



Chalk. — The upper chalk range passes from the heights near Dunstable, through the north-west 

 of Hertfordshire, by Hitchin and Baldock, to Barkway and Royston Downs, and thence by Balsham 

 and Newmarket into Suffolk. Mr. M'Lauchlan informs me that the chalk ridge at Thorfield (about 

 570 feet high) is an anticlinal line, and that the overflow of water in Wardington Bottom, near 

 Newsell's-bury Park, while the rest of the country is dry, renders it probable that some of the 

 lower beds are there brought up to the surface. On the Ordnance maps two ridges are distinctly 

 marked, which meet thereabouts at an angle ; one passing from Berry Barn through Norfield to 

 Barkway Mill (313 feet high), the other, striking off from Thorfield for about a mile towards 

 the north, turns suddenly to the east, to the group of hills above Royston and Burley, and is 

 continued thence to the north-east through Chishill, 470, and Heydon, 480 feet. The lower tract, 

 in the angle between these ridges, from Newsell's to Known's Folly, may possibly be a valley of 

 elevation like those of Kingclere described by Dr. Buckland. 



The outcrop of the lower chalk and chalk marl, is nearly parallel to the range of the upper 

 strata, and to that of the heights above mentioned ; its general course being from the neighbour- 

 hood of Orwell, through Haslingfield, Cherry Hinton, and Bottisham, to Reach on the margin 

 of the Fens. Thence, from about Milden-hall in Suffolk, near the confines of Cambridgeshire, to 

 Hunstanton, on the north-west coast of Norfolk, a distance of about forty miles, the direction of 

 the chalk escarpment is nearly from south to north. 



The chalk which forms the principal part of the lower hills in Cambridgeshire, bears the local 

 name of " Clunch." It is described by Mr. Hailstone as being harder than common chalk, and 

 usually of a grey colour. It affords, as the lower and marly chalk is found to do in many other 

 places, remarkably good lime : and it would seem that some of the lowest beds, which bear the 

 name of Clunch, agree in their properties, as in geological position, with the firestone of Surrey, 



throughout the Isle of Ely under the name of White Gravel, (the latter is Red); and, Mr. Sedgwick 

 states, are older than the beds of flint gravel in Cambridgeshire. 



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