On the Elsworth Rock and associated Strata. 99 



in minute crystals of sclenite and sulphate of barytes, and became 

 extremely hard as we descended. Every now and then, speci- 

 mens were met with of the Ammonites vertebralis, in which the 

 body-chamber was filled with calcareous matter, and the rest of 

 the shell pressed flat, forming what well-diggers call "shapes;" 

 some specimens were also found of the Gryphcea dilatata. From 

 these fossils I was inclined to regard the deposit above the rock 

 as Oxford Clay instead of Kimmeridge — a conclusion afterwards 

 in some degree confirmed by the abundance in which the latter 

 fossil occurred in another section. Indeed, the fossils from the 

 clay immediately above were scarcely to be distinguished from 

 those in the clay below. And so, instead of Upper Calcareous 

 Grit, the phenomenon presented appeared to be that of a lime- 

 stone dividing two beds of Oxford Clay. 



Continuing the digging, the rock was reached; and here, 

 where protected, its appearance is very different from the wea- 

 thered aspect seen by the brook-side. It is a dark-blue homo- 

 geneous limestone, which I can compare to nothing but the un- 

 septarious cement-stones of the clays. The oolitic grains were 

 abundant, and as deeply ferruginous as though they had been 

 exposed to the air ; while scattered irregularly about, branching 

 and interlacing, were masses of undecomposed iron pyrites. A 

 rock of undivided structure, such as that described, will be easily 

 understood to be difficult to work ; and I cannot convey a better 

 idea of its hardness than by stating that, during the ten hours 

 during which two men continued thumping away at it, they 

 succeeded in breaking a five- foot iron crowbar, the iron of one 

 pickaxe, and the handle of another, and did not get up a quarter 

 of a hundred- weight of fragments ; and yet it is so easily de- 

 composed by the weather as to be utterly useless for road- 

 mending, building, or any economic purpose. 



Before the deposition of the superimposed clay, the rock ap- 

 pears to have been much denuded, and consequently its thick- 

 ness is very variable. It is commonly about 3 or 4 feet, though 

 in some places not less than 7 feet. The clay immediately above 

 it is of a reddish brown, and, judging from its contents, appears 

 to be coloured by the rubbing up of the rock below. But 7 feet 

 must not be supposed to be the total thickness of the deposit ; 

 for on the top of it is a clay of about 5 feet in thickness, and 

 then an upper rock of 18 inches, which forms the surface, and 

 above which, at the places where exhibited, there is very little 

 clay. This middle clay is of a brown-black, and is nowhere well 

 exposed ; where best seen, it contained numerous specimens of 

 a small variety of Ostrea Marshii. The rock above it has all the 

 outer characters of that below, being equally rusty and quite as 

 oolitic — except, however, at one point, where, getting a section 



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