408 Rev. T. G. Bonney—On the Roslyn mil Clay Pit. 



into a pre-existing valley. Though no doubt there have been slips 

 from the clifis on the south bank of this valley, I do not think that we 

 can very well explain the position of this mass of Chalk, especially 

 at the south-east corner, on the first of these theories. Moreover, I 

 do not think that we anywhere find the Gault conformable with the 

 Neocomian sands ; the former appears to me to be of variable thick- 

 ness, and to be merely the base of the great fragment to which it 

 is attached, seeing that it rests, now on Boulder-clay, now on Kim- 

 meridge Clay, now on (disturbed) Neocomian sand. 



But it may be said there is no precedent for such a huge trans- 

 ported mass. Mr. Seeley ridicules the idea (Geol. Mag., Vol. V., 

 p. 347) ; although he quotes in a former paper (Geol. Mao., Vol. I., 

 p. 150) a case of a very large mass of Chalk, 180 feet long, included 

 in the Boulder-clay of Norfolk. Mr. Fisher also (Geol. Mag., Vol. 

 v., p. 409) mentions, without measurements, some other masses which 

 are evidently very large. But in the Quart. Journ, Geol. Soc, vol. 

 ix., Prof. Morris describes a boulder in the Lincolnshire drift (which 

 according to his account much resembles that at Ely, even to its 

 showing traces of stratification and an upper and lower division) 

 in the following words (p. 320) : — " Emerging from the south end 

 of the tunnel on the Great Northern Eailway, which is 880 yards 

 long, we see the drift on either side of the cutting, buoying up an 

 enormous irregular mass of Oolitic rock, through which the cutting 

 has passed; this mass is 430 feet long, and at its deepest part 30 feet 

 thick." He says, "that the beds, though broken and disturbed, 

 retain to some extent their relative positions, and belong to the lower 

 part of the Oolitic rocks of the district." And this statement Prof. 

 Eamsay indorses (Quart. Journ. Geol. Soc, vol. xxvii., p. 252), 

 calling the boulder 380 yards in length ; stating also that Mr. Judd 

 has discovered large masses of erratic marlstone, and that Prof. 

 Geikie is of opinion that the Lias of Linksfield is also an erratic. 



Hence the boulder theory, startling as it may seem at first sight, 

 appears to me to present far less difficulty than that which accounts 

 for the phenomena by a series of faults. The facts which I have 

 brought forward are in my opinion very strongly in favour of Mr. 

 Eisher's hypothesis ; and my only excuse for bringing the subject 

 under the notice of the Society is that as left by him it was rather an 

 hypothesis than a demonstration ; more facts were wanted, and these 

 time has, I hope, enabled me to supply. To sum up briefly, the 

 question now stands thus : — (1) Either there are faults — this I have 

 tried to show is all but impossible ; or (2) there has been a landslip 

 from a Chalk cliff overhanging a valley in the Kimmeridge Clay, and 

 the Chalk once on Eoslyn Hill has since been denuded away ; or 

 (3) the mass is an included Boulder, and has been brought to its 

 present position on an ice raft. I think the facts accord best with 

 this, and that there is no fourth hypothesis probable. The only point 

 on v/hich I differ from Mr. Fisher — and it is a very small one — is that 

 I think the valley existed before the great boulder arrived, and was 

 not ploughed out by the keel of its icy ship. 



