Vol. 55.] LIMESTOJTE-KNOLLS IN CEAVEN. 349 



formed of arenaceous rock. I have notes of a grit-breccia in the 

 canal-bank at Skipton, and also in Little jSTewton Gill, near Long 

 Preston. 



The production of breccias which frequently simulate conglo- 

 merates as the result of earth-movement is now well established. 

 Many years ago I published some notes on rocks which often show 

 a brecciated structure of this character, occurring in the neigh- 

 bourhood of Ilfracombe,^ and Mr. Lamplugh's paper on the crush- 

 conglomerates of the Isle of Man,^ where the author quotes other 

 cases of somewhat similar structures, will be fresh in the memory 

 of Fellows of the Society ; in the discussion I mentioned the 

 discovery by Mr. Harker and myself of crush-breccias having similar 

 characters in the Ordovician rocks of Lakeland. 



I need hardly say that, as with the knolls, so with the breccias, 

 actual inspection of the sections is much more important than 

 examination of the evidence yielded by hand-specimens, diagrams, 

 and reproductions of photographs. 



VI. COMPAEISON OF THE DEPOSITS ON BOTH SIDES OF THE FaULTS. 



On p. 828 is tabulated Mr. Tiddeman's correlation of the 

 deposits on the two sides of the fault-system. It has been made by 

 one who has devoted many years of his life to detailed mapping of 

 the Carboniferous rocks, and is therefore not lightly to be set aside. 

 Nevertheless, I venture to make a few remarks upon the subject. 

 As the type of rock suddenly changes at the faults, the correlation 

 cannot be the result of actual tracini^ of the beds from one area into 

 the other. Nor can it altogether depend upon palaeontological 

 evidence, for the faunas of the beds on the south side of the faults 

 seem to differ markedly from those on the north side. Lithological 

 characters may furnish some clue, even though it be admitted that 

 they differ greatly in the two areas. 



It is an interestiDg fact that the limestone-fauna of the area 

 south of the faults is far richer than that of the district on the 

 north side, but experience leads me to state that as a rule limestones 

 in an area that has been subjected to erogenic disturbances of 

 the type which, according to my view, gave rise to knoll-structure, 

 are richer in fossils than those that have undergone epeirogenic 

 movements only. ' Richer in fossils,' I have written, but the state- 

 ment should be qualified, and the term ' richer, in fossils which can 

 be readily extracted in a perfect state,' substituted. The horny 

 and compact limestones of a district are often seen to be crowded 

 with fossils, which are exposed in cross-sections when the rock is 

 fractured, but these fossils can be rarely extracted so that their 

 specific or, in many cases, even generic characters can be deter- 

 mined, and consequently the fauna of a rock which is seen 

 to be entirely formed of organisms of various kinds may remain 

 practically unknown. The instinct of the fossil-collector which 



1 Geol. Mag. 1888, p. 218. 



2 Quart. Journ. Geol. See. vol. li (1895) p. 563. 



