289 
1911-12.] Report on Rock Specimens. 
Jurassic rocks are probably represented by eight small fragments of 
fossiliferous sandy limestone, like those from Station 3 of the Knight 
Errant. 
The Cretaceous formation yields one small specimen of chalk and a 
piece of calcareous rock with casts of sponge spicules. 
Of doubtful age and origin are two specimens of white marble. 
To the Lewisian gneiss may belong eight specimens of granular horn- 
blende and biotite-gneiss of Cape Wrath type, and one of pegmatite with 
felspars converted into agalmatolite in the manner that happens on the 
mainland where the Cape Wrath assemblage of gneisses is overlaid by 
Cambrian quartzites. A specimen of chloritic schist with bladed actinolite 
suggests a metamorphosed calcareous sediment. Rocks of this latter type 
occur with the Moine schist and Dalradian rocks of the mainland and of the 
Shetland Isles. 
Igneous rocks are represented by two small fragments of granite, one 
with biotite and one with hornblende. No less than fifteen specimens of 
dolerite and basalt occur ; one of olivine dolerite measures 4 inches in 
diameter. 
The mode of occurrence of the stones from the dredgings of H.M.S. 
Knight Errant and Triton along the Wyville Thomson ridge and the 
Faroe Bank suggests that they have been embedded in a kind of boulder 
clay, and have been exposed on the sea-bottom by strong currents that 
have passed over the ridge. Not only is there the warm-water drift 
passing eastwards, driven forward by the prevalent westerly winds, but 
strong tidal currents press backwards and forwards daily over a great part 
of the ridge. 
The stones are or have been for the most part glaciated, and many of 
them still retain their striations. The portions of the ridge examined 
appear to be of the nature of a moraine profonde * This deposit was 
probably produced by the great ice-sheet which, emanating from the 
mainland of Scotland, combined with the Scandinavian ice and, filling the 
North Sea, passed westwards over Caithness, Orkney, and Shetland to 
beyond the Wyville Thomson ridge, receiving further accessions of ice 
from North Sutherland by the way, before reaching water sufficiently 
deep to break it up into icebergs.! The assemblage of stones in the 
dredgings strongly favours this view. The Lewisian gneisses, Torridonian 
arkoses, Cambrian quartzites, and “ Moine schists ” from the rocks of the 
* Proc. Roy. Soc. Edin ., vol. xi., 1882, p. 649. 
t Brit. Assoc. R&port for 1885, Trans, of Sections : “Further Evidence of the Extension 
of the Ice in the North Sea during the Glacial Period,” by B. N. Peach and J. Horne. 
VOL. XXXII. 19 
