706 EEPORT— 1887. 



their lithological characters (using the phrase in a wide sense), may ultimately 

 prove to be possible. 



(7.) The views already expressed by the author as to the distinctness of 

 cleavage-foliation and stratification-foliation have been fully confirmed by the 

 examination of the above districts. He believes that the failure to recognise this 

 distinction is the cause of the contradictory statements with regard to the relation 

 of foliation and bedding which have been made by so many excellent observers, and 

 lies at the root of much of the confusion which exists on the subject of the so- 

 called metamorphic rocks. 



5. Some Effects of Pressure on the Sedimentary EocJcs of North Devon. 

 By J. E. Marr, M.A., F.G.S. 



The structures described in this paper are mainly seen in the Ilfracombe 

 division of the Devonian system, as exposed near the bathing-place at Ilfracombe. 

 The rocks there consist of argillaceous beds with thin bands of grit and crinoidal 

 limestone ; these harder beds are folded into a series of small sigmoidal folds, which 

 form portions of similar larger folds. When the middle limb is replaced by a 

 fault, the cores of the folds remain as ' eyes ' of limestone or grit, and these ' eyes ' 

 have undergone further modification, having been pulled out into thin lenticular 

 masses. In this way we have all the mechanical structures of a true schist pro- 

 duced (including the apparent false bedding), the rock now consisting of clay-slate 

 with alternating folia of grit or limestone, or both. 



Quartz veins are folded in a similar way to that described above, and the final 

 result of this folding appears to be the production of a rock consistmg of alternating 

 clay-slate, limestone, and quartz folia. 



Every stage of the process is seen in the case of the limestone 'eyes.' The 

 cores of limestone when not dragged out have their component crinoid stems 

 pressed into polygons, which have been formed in the way described elsewhere by 

 Dr. Sorby. When the limestone is pulled out the stems are separated, as in the 

 case of the belemnites figured by Heim, and the intervening portion is filled with 

 calcite. 



In this neighbourhood, then, we find sedimentary rocks presenting all the 

 mechanical peculiarities of normal schists, without any great amount of chemical 



6. Report of the Committee appointed to investigate the Microscopical Struc- 



ture of the older Bocks of Anglesey. — See Reports, p. 230. 



7. Notes on the Origin of the Older ArchcBan Rocks of Malvern and 



Anglesey. By Charles Callaway, D.Sc, F.G.S. 



The author had recently communicated to the Geological Society of London a 

 paper in which he contended that certain crystalline schists of the Malvern Hills 

 had been formed from igneous rocks. This conclusion was now extended to all the 

 foliated rocks of the district. The metamorphism was zonal, the schistosity being 

 usually confined to bands, wbich occurred most frequently where the rocks were 

 interlaced with veins. The most important shear-zones were those in which 

 diorite was penetrated by granite-veins. The following were the principal changes 

 normally observed in approaching a shear-zone : — 



(1) The rock acquired a parallel structiu'e. 



(2) This change was often accompanied by an apparent corrosion of the 

 hornblende and felspar, numerous perforations appearing in the crystals, and their 

 margins presenting curvilinear outlines. This efiect seemed due to loss of bases, 

 since it was attended by a corresponding development of quartz. 



(3) The hornblende was replaced by black mica, the necessary potash being 

 presumably derived from the felspar of the adjacent granite-veins, which were 

 often extremely quartzose. 



