Dr. FiTTON on the Strata below the Chalk. 307 



borders of Cambridgeshire, at Gamlingay, with Gault resting upon it ; " and in some of the pits, 

 "the line of junction is as well defined as that of two immiscible fluids"; but the sand contiguous 

 to the clay is more highly impregnated with iron than the lower part, and is cemented by the oxide, 

 so as to form a hard rock. Leaving to the south-west the two villages of Hatley, both on 

 the Gault, the boundary passes between Little and Great Gransdon, and west of Caxton, (which 

 is on the clay), through the north-west sides of the parish of Eltsley, by Passworth St. Everard's, 

 and Passworth St. Agnes, to Hilton and Fenny Drayton. Li the parish of Fenny Stanton and 

 that of Croxton, a bed of clay (Gault?) rests on the sand. The sand can be traced across the 

 lower country, in a direction nearly parallel to the chalk, from Caxton (Section No. 22.) by Co- 

 nington, and Long Stanton, through Cottenham and Denny Abbey, where the surface is occuf)ied 

 by low hillocks of gravel ; and on the north of those places it forms the summit of many of the 

 heights of small elevation on the south-eastern verge of the Fens. Thus at Haddenham, the hill, 

 133 feet high, is capped with sand ; and the prolonged height, or ridge thence to Aldreth, called 

 "the Sandy-way," about 122 feet, is likewise composed of it. The junction of the sand and 

 subjacent clay is well seen, Mr. Sedgwick states, at the clay-pit on the east of Ely ; and sand 

 is visible in the drains from about the fifth to the ninth milestone, along the road from Littleport 

 towards Downham, cutting across the Fens on the north-east of Ely, in a direction corresponding 

 to the previous course of this formation near Cambridge. 



Kimmeridge clay. — This occupies all the lower tract on the north and west of the line of sands 

 above mentioned, as on the course of the Ouse, or Old West river, from Fenny Stanton and Ho- 

 lywell on the west, to its junction with the Cam at Thetford, and thence towards Ely. Sec- 

 tions are of necessity rare ; but a very good one, exhibiting the junction of the clay and Lower 

 green-sand, is exposed in the pits east of Ely. On the west and south-west of Ely the clay is 

 capped in many places by sand, in the form of outliers, on the summits of the heights, which here 

 range from about 120 feet to 50 (see the list in the Appendix C.) : and the clay is continued 

 uniformly through their bases, to a point north-west of Haddenham, on the road to Chatteris, 

 where it is succeeded by the Oxford oolite. 



Oxford oolite. — A remarkable exception to this uniformity of structure occurs at Upware, on 

 the Cam, about three miles north-west of Reach (see the Section, Plate X. a. No. 24.) ; where the 

 upper strata of the Oxford oolite make their appearance, in a low ridge extending for about three 

 miles north of Upware, in a direction nearly parallel to that of the Cam, which is here not much 

 more than 12 feet above the sea at low water. The stone beds have been opened here in two or 

 three quarries ; a very large one being near the river, and on the line of the section 24. The 

 strata are slightly inclined to the west of north, in a direction opposite to that of the beds below 

 the chalk. The stone here laid bare to a depth of about 10 or 12 feet, consists of a loose rubbly 

 limestone, of a cream colour, in some places coarsely oolitic, and containing many of the charac- 

 teristic fossils, for a collection of which I am obliged to Professor Sedgwick and Mr.M'Lauchlan : — 

 Spines of Cidaris ; Corals ; an Area ; Fusus, a new species ; Gervillia aviculoides ; Isocardia, 

 an acute species ; Modiola; Ostrea gregarea ; Pecten viminalis; Plagiostoma ; Plicatula; Turbo 

 muricatus, &c. 



The coralline beds (the proper " Coral rag" of Smith) do not come up to the surface at this 

 place; but they break out, Mr. Sedgwick informs me, beyond Haddenham, going towards Chat- 

 teris ; and he suspects that the shelly beds of this formation occur in some other places in the 

 county, between the Kimmeridge and the Oxford clays, from the occurrence of numerous bits of 

 the coral rag and of its fossils in the brown clay, which masks so much of the surface of Hunting- 

 donshire and Cambridgeshire, and in a condition which makes it probable that they had not been 

 drifted far. 



