408 Fisher — Roswell Hill Clay-pit, Ely, 



I will first of all consider the presence of the Chalk-marl and the 

 clay on the northern side of the pit. 



I have said they are clearly in sequence. Their junction is per- 

 fectly natural. The Chalk-marl becomes sandy, and contains a few 

 scattered nodules of jihosphate of lime, with some of the fossils of 

 the Upper Green-sand usual in the neighbourhood of Cambridge, 

 and then the clay succeeds. The character of the beds here has been 

 so well described by Mr. Seeley,^ that I need not say more about 

 them, except that I think it open to question whether the clay is 

 really Gault. There is about Cambridge a band of clay in the lower 

 part of the Chalk, which was well shown in the construction of the 

 waterworks at Cherryhinton, and I am rather inclined to think that 

 the Ely clay belongs to the same bed. I recollect phosphatic 

 nodules occurring in connection with it at Cherryhinton. I think 

 the abundance of shells, and especially of Perna, in the Ely clay, 

 rather militates against its being Gault, but I merely throw this out 

 as a suggestion.^ 

 Boring by Mr. Docwra at Cherryhinton Waterworks noted in 1854. 



ft. in. 





ft. in. 



Soil 1 



Clunch 



. ... 6 



Plastic 29 



Sand 



. ... 8 



Upper Green-sand with fossils 10 



Gault not pierced ... . 



. ... 45 



82 6" 



I visited the spot and found Belemmtes in the "Plastic," and co- 

 prolites from the supposed Upper Greensand. From a subsequent 

 cutting made to convey water from near Mr. Okes's house, I recol- 

 lect observing that the above-mentioned " plastic" was a stratum in 

 the clunch. This section makes a coprolite layer beneath the clay. 

 There may also be one above it. 



At any rate we may look at the Chalk and clay near Ely as a 

 single mass, and whatever accounts for the presence of one will 

 equally account for the other. In short they are a large mass of 

 Cretaceous beds in a nearly vertical position, with Boulder-clay 

 abutting upon them. The curved lines of junction as seen in the 

 section are nothing more than the curves formed by the intersection 

 of the surface of the workings with a nearly plane surface of junction 

 between the Chalk and the Gault, dipping at a very high angle 

 towards the north. 



Now there are two ways of accounting for the presence of this 

 Cretaceous mass. It is either brought up by a fault with reference 

 to the Boulder-clay, but down with reference to the Kimmeridge, or 

 else it is a huge iDoulder, forming as much an integral part of the 

 Boulder-clay as any block of Oolite or flint which it contains. 



Mr, Seeley appears to consider its presence best accounted for by 

 a fault, but I think I shall be able to show that the other is the 

 more probable explanation. 



1 Geol. Mag., Vol. II., p. 529. 



2 At a subsequent visit, 26 April, 1867, I saw the Lower Green-sand in sequence 

 to this clay, which would make it the true Gault. In another part of the pit the 

 Gault reposed on Boulder-clay with Chalk pebbles. 



