B. 11. Tiddeman — Formation of Reef Knolk. 21 



iirea of the downthrow side and from other considerations there was 

 every reason to suppose that the Craven Faults were actually taking 

 place during the formation of those rocks. 



My friend Mr. J. E. Marr, F.E.S., has in a most courteous way, 

 ■whilst taking my geological mapping as for the most part correct, 

 found reasons for dissenting from all the groundwork on which it 

 was founded.' In combating Mr. Marr's views I offer no opinion 

 on knolls of other localities or other ages which he brings forward 

 in support of his views. I speak only of the Carboniferous knolls 

 of which I have written, and with which I am well acquainted. 

 Speaking generally, 1 think the differences between us may be thus 

 summarized : — 



1. Mr. Marr disagrees with my reading of the succession and 

 thickness of the rocks on the south side of the Craven Faults, and, 

 whilst I consider that we have two distinct successions of different 

 thickness caused by a difference in the rate of submergence in the 

 two districts, and by shallower and deeper seas, he regards the 

 Tocks on both sides as having been one series of like thickness in 

 orderly sequence to the north, but, so to speak, shuffled by earth- 

 movements on the south of those faults and repeated several times 

 by overthrusts. 



la. In illustration let us take a pack of cards, say arranged in 

 suits as representing the regular country on the north side, and 

 several packs similarly ai"ranged to represent the greater thickness 

 on the south side. Shufifle these last to represent the supposed 

 disturbance and overthrusting. Shall we always find after 

 shuffling the same general succession ? Yet over a tract reaching 

 from Draughton to Chipping and from Settle to Derbyshire, we do 

 get such a general succession, and that does not at all resemble the 

 succession on the north side of the faults. The overthrusting to do 

 this effectually must cover the whole of this wide area comprised in 

 three or four counties, and not confine its operations to a narrow 

 disturbed belt near the Craven Faults. Is Mr. Marr prepared to 

 3nake his orogenic movements extend over so large an area, and 

 thereby arrange the whole country, which they bi*eak up, into so 

 orderly a disposition? 



2. Mr. Marr regards the great difference between the black and 

 white limestone, the form and constitution of the reef-knolls, the 

 abundance in them of perfect fossil forms in a well-preserved state, 

 the conglomerates and breccias which accompany them, as all being 

 the result of what he calls orogenic movements ; in other words, of 

 the folding repetition and overthrusting of the rocks, with here and 

 there relief of pressure. More especially is the last called in as 

 being the reason for the abundant and well-preserved fossils and the 

 change of the limestones. 



It is extremely difficult for me to accept these views. If we could 

 believe that a black, well and thinly bedded limestone can by any 

 ^physical change be converted into a white crystalline mass with 



' Quart. Joui-n. Geol. Soc, vol. Iv, pp. 327-3G1. 



