CRUISE IN LOCH FYNE, JUNE, 1899. 373 



Pu2)a cylindracea (Da Costa) [ = P. umbilicaia, Drap.] Eilean 



Aoghainn, dead. 

 Clausilia 2)erversa (Pult.), Eilean Aoghainn. 



C. perversa, var. tutnidula, Jeff. Glas Eilean and Eilean Ao- 

 ghainn. 



GEOLOGY, ETC. — The first four islands on which we landed, 

 Sgat Mohr (the big skate), Eilean Buidhe (the yellow isle), Eilean 

 Buic (buck isle), and Caisteal Aoidhe (said to mean Hugh's castle), 

 or the "Robbers' Rock," an island only at half- tide, belong to a 

 group of rocks which in the Cowal mainland consists of albite 

 schists, schistose greywackes, and other mica-schists very highly 

 metamorphosed. Mr. W. Gunn, in the Geological Survey Memoir 

 on Cowal, page 196, says — "Moderately fine grey micaceous schist, 

 full of quartz veins and much plicated in places, forms the island 



of Sgat Mohr " "A N.N.E. crush crosses Sgat 



Mohr." Two specimens are exhibited from this island, both 

 of quartzose micaceous schist, one of them very much 

 plicated, and with quartz veins. The crush of which Mr. 

 Gunn speaks, is presumably the cause of a depression which 

 runs across the island, and is seen continuing in the same 

 direction on the mainland — the rock on each side of the crush 

 being more broken, and thus more readily worn away by rain, 

 frost, etc. Next are shown two specimens of mica-schist from 

 Eilean Buidhe, which lies almost in the centre of an " anticline of 

 foliation." From Caisteal Aoidhe there is exhibited a piece of 

 mica-schist, or quartzose muscovite biotite schist, probably a 

 metamorphosed greywacke. From the vitrified fort on this 

 peninsula several specimens are exhibited, showing pieces of rock 

 fused together. 



We do not know anything of the history or traditions of this 

 fort, but the name " Robbers' Rock " suggests that it may be a relic 

 of its possession by invading strangers, such as the Norsemen, 

 whose galleys frequented these coasts seven to ten centuries ago, 

 and of whose presence we have enduring evidence in the name of 

 the place where we lay on the first night of our cruise — namely, 

 Skipness, or ship nose or point, and in that of the bay behind 

 Sgat Mohr, Asgog, said to be askr vik, or ships' bay. 



The other four islands which we visited, belong to a series of 



