On Limestone- Knolls in the Craven District. Iti3 



nor true spinel has been previously recorded from the limestone or 

 from Scotland at all. The three cr tour bands of limestone which 

 make their appearance on Sheets 123 and 127 of the 6-inch 

 survey of Ross-shire are probably the same bed repeated by isoclinal 

 folds. The banded gneisses, schists, and eclogites among which the 

 limestones occur are separated from the sheared and inverted Torri- 

 donian rocks on the west-north-west by flaggy granulitic quartzite 

 aud siliceous mylonite, the latter being next to the Torridonian 

 rocks and lying along the line of a great post-Cambrian thrust, 

 traceable from Oronsay to near the Point of Sleat. On the eastern 

 side of the mylonite all the rocks of sedimentary aspect are 

 greatly altered, and the gneisses and schists associated with the 

 limestone resemble parts of the Lewisian gueiss. The quartzite- 

 series is repeatedly folded with the gneissose series ; but although 

 the precise relationship of the two has not been made out, rocks 

 of different characters lie next to the quartzite in different places, 

 while the alteration-products which characterize the limestone are 

 found in contact with the quartzite at one or two spots. In the 

 limestone, pieces of diopside aud a serpentine-like mineral are so 

 abundant that they may equal the rest of the rock in quantity. 

 The mass of the limestone is but little affected by movement, thus 

 offering a strong contrast to the Loch Maree limestone. The 

 forsterite and spinel are in part associated together in lumps, from 

 which they were separated by means of heavy solutions for analysis. 

 The spinel in hand-specimens is of an almost opaque blue colour, 

 and some examples show small crystal-faces. That seen in micro- 

 scopic slides is shapeless and colourless, except that the blue 

 portions appear brown by transmitted light. Analyses of the two 

 minerals are given at the close of the paper ; and it is pointed out 

 that the spinel is like that of Aker in colour and mode of occurrence. 



Apiil 26th.— W. Whitaker, B.A., F.R.S., President, in the Chair. 



The following communication was read : — 



1. ' On Limestone-Knolls in the Craven District of Yorkshire 

 and elsewhere.' By J. E. Marr, Esq., M.A., F.K.S., F.G.S. 



The author begins with a geucial account of the district, partly 

 founded on the published work of Mr. 11. H. Tiddeman, but sub- 

 stantiated by his own observations. The Lower Carboniferous 

 rocks north of the Craven Fault-system differ in character and 

 thickness from those on the south ; they exhibit little disturbance 

 on the north, but on the south they are thrown into a series of folds, 

 while it is also on this side that the knobs of limestone called knoll- 

 reefs by Mr. Tiddeman occur. In order to illustrate the nature of 

 the disturbances south of the Craven Faults, the folds of Draughton 

 Quarry are described in detail. In addition to the anticlines and 

 syncline usually figured, there occurs, on the north side of the 

 quarry, an overfolded anticline with a faulted core. One of the 

 calcareous lands is really a limestone-breccia, which appears to have 

 been broken by earth-movement before the rocks were folded. The 

 top and base of the breccia and of other hard bands, together with 

 the joiut- faces, are traversed by slickensides which were hori- 

 zontal before the folding. Microscopic examination of the lime- 

 stones shows that they exhibit various stages iu crushing with 



