362 DE. W. HIND AND MR. J. A. HOWE ON THE [Aug. IQOI, 



latum — that is to say, in their proper position with respect to the 

 knoll-forming limestone below. 



Of the two conflictiDg views of the origin of the knoll-structure, 

 namely, the ' reef-knoll theory ' of Mr. Tiddeman ^ and the ' thrust- 

 hypothesis ' of Mr. Marr,^ we are inclined to accept the former, after 

 certain modifications. We agree with Mr. Tiddeman that there is 

 something essentially reef-like in the mode of formation and shape 

 of the knolls and in the materials of which they are made ; they 

 seem indeed to closely resemble certain reef-structures now forming 

 on the East Coast of Africa. At the same time, we cannot see 

 in them a structure such as he demands, namely, a horizontal 

 central bedding, with peripheral periclinal slopes. Hill Skelter- 

 ton, Swinden, and Butterhaw, and a smaller unnamed hill to 

 the west, are distinctly bedded throughout, without any quaqua- 

 versal dips ; while on Hill Stebden and El [Hill ?] Bolton the 

 bedding seems too obscure to permit of the formation of any 

 definite decision. On Keal Hill the principal direction of dip 

 seems to be to the south-east, and this, with a very small fault, 

 would allow the beds to pass regularly beneath the Grits of Burnsall 

 Fell. Again, we have not yet been able to find any of the con- 

 glomerate which, Mr. Tiddeman says, fell down from the reef and 

 became embedded in the shales round the base. That such a con- 

 glomerate should exist is exceedingly probable, yet at the best 

 exposure mentioned by him, in the stream-section east of Keal 

 Hill, we failed to discover it. What we found was the following 

 section : — 



Feet. 



Shales 20 



* Band of (crushed ?) limestone 3 



Dark shales 3 



* Band of crushed limestone, with Cladodus 3 



Shale, with Biscites (stdcatus ?) , 1 



Black shale, with Posidoniella Icevis and crushed 



goniatites. 



The bands of limestone marked with an asterisk probably represent 

 Mr. Tiddeman's ' conglomerate,' but they appear to us to be bands 

 of dark limestone, in parts crinoidal, slightly shattered, probably 

 by the fault suggested above. They do not in any case suggest the 

 appearance, or contain the fossils, of the knoll-limestone. 



With regard to Mr. Marr's views, we admit that anyone coming 

 to the examination of these curious structures with a vis a tergo 

 produced by an hypothesis of thrusts, would see much in his favour, 

 but nothing, we believe, that could be taken as conclusive evidence 

 or that could not be matched in many of the similar limestones in 

 undisturbed areas. 



^ Brit, Assoc. Eep. 1889 (Newcastle) p. 602 ; Brit. Assoc. Excursion Guide, 

 Leeds, 1890 pp. 47 et seqq. ; Oomptes-rendus du IVeme Congres geol. internat. 

 1888 (London) pp. 321-22 [publ. 1891]. 



2 Quart. Journ. Geol. Soc. vol. Iv (1899) p. 327 ; see also Mr. Tiddeman's 

 criticism, Geol. Mag. 1901, p. 20. 



