290 Proceedings of the Royal Society of Edinburgh. [Sess. 
mainland of Sutherland or from their extension northwards, now either 
under sea, or in the Northern Isles, are well represented. In addition are 
found the peculiar locally developed types of the Old Red Sandstone rocks 
of Caithness, Orkney, and Shetland, which form a considerable percentage 
of the dredged stones, while Secondary rocks of types unknown in the 
west of Scotland but which are to be found in situ on the east coast, and 
are known to occur below sea and also in South Sweden and Denmark, 
along the path of the great ice-sheet, occur plentifully at all the stations. 
The few Carboniferous rocks and the dolerites may have come along with 
the ice from the Carboniferous areas of Central Scotland, or the extension 
of those rocks eastwards under the North Sea. 
A like assemblage of fossiliferous Secondary and Carboniferous boulders 
was met with in the shelly boulder clays which are found in Caithness and 
Orkney,* but rocks of these types are apparently absent from Shetland.-]* 
The evidence obtained by the Michael Sars from Stations 100 and 
101 is also in keeping with this view and affords it additional support. 
The specimen of sandstone from Station 101 is like the Brenista flags of 
Shetland,^ while the examination of the blue mud from Station 100 in the 
“ Challenger ” office shows that it contains 30 per cent, of minerals, the quartz 
grains being “ tinged red ” or with “ green chloritic tinge.” The red quartz 
grains are in all probability derived from Torridonian or Old Red Sand- 
stone, and the green from the. Lewisian gneiss where it has undergone 
decomposition in pre-Torridonian time, or from the “ Epidotic Grits ” so 
common in the basement members of the Torridonian system. “ Tourmaline, 
biotite, and orthoclase,” the other minerals found in the mud at these Stations, 
also point to some source such as the Lewisian gneiss. Fragments of black 
and red slaggy lava and volcanic glass also occur, suggesting that they had 
come from Iceland or Faroe. The commingling of these materials suggests 
the work of floating ice beyond the limit of the great ice-sheet. 
The occurrence of such a number of dead and decaying shells of shallow- 
water habitat at Station 3 ( Knight Errant) in fifty-three fathoms affords 
evidence of a widespread subsidence of the land and of the sea-bottom. 
The absence of the higher raised beaches in Caithness, Orkney, and Shet- 
land, together with the occurrence of submerged peat-mosses within the 
same area, and also in the north of the island of Lewis, all point to such 
* B. N. Peach and J. Horne, “ The Glaciation of the Orkney Islands,” Quart. Journ. 
Geol. Soc., yoI. xxxvi. p. 648, 1880. “The Glaciation of Caithness,” Proc. Roy. Phys. Soc. 
Edin ., vol. vii. p. 307, 1881. 
t B. N. Peach and J. Horne, “ The Glaciation of the Shetland Isles,” Quart. Journ. Geol. 
Soc., vol. xxxv. p. 317, 1879. 
X See ante. 
