Vol. 55.] IIMBSTONE-KNOLLS IN CRAVEN. 363 



knolls so magnificently exposed on the foreshore of Poolvash Bay in 

 the Isle of Man. His impression had been that these knolls were 

 original structures ; and after careful re-examination he still failed 

 to see how they could be accounted for otherwise, though he would 

 admit that there was evidence of lateral movement in the rocks in 

 the vicinity. That columnar masses of limestone might accumulate 

 among shales was proved by the ' Tepee Buttes' of Colorado. If an 

 area in which lenticular masses occurred were subsequently disturbed, 

 he thought that all the phenomena described by Mr. Marr might be 

 produced. He regretted that the relation of the palaeontology of the 

 knolls to that of the surrounding beds had not been discussed, as it 

 seemed of vital importance. 



Prof. SoLLAs recognized the value of the observations, and the 

 ingenuity of the explanation so clearly set forth by Mr. Marr ; he 

 thought, however, that insufficient allowance was made for the 

 general tendency of corals and calcareous algse to assume reef-like 

 forms. Some steps appeared to be missing in the argument that 

 crystalline limestone, distinguished by the exceptioTially perfect 

 state of preservation of its included fossils, had assumed the crys- 

 talline state owing to relief of pressure. If this meant that a dimi- 

 nution had followed an excess of pressure, the crystalline state 

 might be accounted for, but not the preservation of the fossils : if, 

 on the contrary, it meant that the knolls had been sheltered from 

 the excessive action of pressure, the preservation of the fossils was 

 explained, but not the crystalline state. It seemed more probable 

 that originally reef-like growths had consolidated before movement 

 took place ; if these, with their associated conglomerates, were 

 buried in sediment, and then subjected to rock-folding and flow, 

 just such phenomena as had been described would naturally 

 result. 



Mr. Strahan regretted that no one present had seen both the 

 Isle of Man and the Yorkshire sections. The structures seemed, 

 however, to be similar ; and those in the Manx Carboniferous Lime- 

 stone were certainly, in his opinion, of contemporaneous age, and 

 not due to subsequent movement. It was noticeable that the knoll- 

 reefs were of local occurrence, and did not exist in many places 

 where there was evidence of much thrusting, as, for example, along 

 the Dent Pault. The conglomerates exhibited by Mr. Marr did not 

 resemble fault-rock, but contained what seemed to be true rounded 

 pebbles or nodules, nor did it appear possible that limestone-bands 

 could have been so folded as to completely envelcJp a nucleus, as was 

 the case with many of these nodules. Conglomeratic bands of this 

 nature, moreover, were not uncommon in the Carboniferous Lime- 

 stone in other districts, where there was no suggestion of earth- 

 movements. At the same time, Mr. Marr had produced abundant 

 evidence of the effects of earth-movement in the area which he had 

 described, and it seemed likely that the original structures in the 

 limestone had been somewhat modified thereby. 



The President, Dr. Sorby, and Prof. "Watts also spoke. 



