On an Inlier among Jurassic Rocks of Sutherland. 423 



softened and metamorphosed ; or possibly ab initio truly igneous 

 Tocks, and related to the charnockite-magma. Reasons for and 

 against these views are given. The relations between the crys- 

 talline limestones and nepheline-syenites of Alno have suggested to 

 Prof. Hogbom that perhaps the limestone may have been a product 

 of the nepheline-syenite magma there. 



The author feels sure that the crystalline limestones of Ceylon 

 have not arisen by the alteration of the basic lime -silicates of the 

 pyroxene-granulites, although Prof. Judd has advanced this theory 

 in connection with the crystalline limestones of Burma, which 

 seem to resemble those of Ceylon in many ways. 



2. ' On Proterozoic Gasteropoda which have been referred to 

 Murchisonia and Pleurotomaria, with Descriptions of New Subgenera 

 and Species.' By Miss Jane Donald. 



March 26th.— Prof. Charles Lapworth, LL.D., F.R.S., President, 

 in the Chair. 



The following communications were read : — 



1. 'Ona remarkable Inlier among the Jurassic Rocks of Suther- 

 land, and its Bearing on the Origin of the Breccia-Beds.' By the 

 Rev. John Frederick Blake, M.A., F.G.S. 



On the coast of Sutherland due south of Port Gower is seen 

 •on the scars at low water a long rocky crest of Old Red Sandstone, 

 with its flaggy beds dipping at a high angle. It is of considerable 

 height, and is surrounded by nearly horizontal Jurassic beds con- 

 taining large blocks of rocks similar to those of the crest, irregularly 

 placed. The size, outline, and relation to the surrounding rocks 

 show that this cannot be a transported block, but must have been 

 part of, or directly derived from, a neighbouring coast — like the 

 modern sea-stacks of the present coast at Duncansby. 



The relations of the Jurassic rocks to the Old Red Sandstone are 

 seen in the Gartymore Burn. The fragments of the latter contained 

 in beds of the former become more numerous as the junction is 

 approached, and ultimately form the whole mass — as would happen 

 in the case of a cliff-talus. It is concluded that the breccia-beds 

 may in part have originated on the spot. 



The distribution of the breccia-beds in the Jurassic Series is then 

 considered in detail. Three horizons can be traced in this series, 

 namely, the zones of Cardioceras alternans, Hoplites eudo.vus, and 

 Perisphinctes Pcdlasi. No breccia-beds are found in the first of these, 

 but there are sporadic ones in the second, within which the inlier 

 occurs, and they become very numerous in the third. The ordinary 

 autochthonous fossils, including plant-remains, occur in the inter- 

 vening shales, but the breccia-beds themselves contain only large 

 heterochthonous fossils, including Rhynchonellas and corais, and 

 where these occur intermediate beds are found, composed of crushed 

 organisms. North of Helmsdale one breccia-bed has apparently 

 squeezed up the underlying shale into an anticlinal arch, against 

 another boss of Old Red Sandstone. 



