360 ON THE RED SANDSTONE, MARBLE, 
Ocean. And it is worthy of being noted, as bearing on our 
question, that the Scottish Lias of the Atlantic holds —as at 
Broadford and Applecross — exactly the same relation to the 
Red Sandstone of the west coast that the Scottish Lias of the 
German Ocean does to the Old Red Sandstone of the east. 
Both Red Sandstone deposits may be equally described as 
resting on the gneiss and overlaid by the Lias. Further, I 
may be permitted to ask, to what system known to the geolo- 
gist does the Red Sandstone of our north-western coasts 
belong, if not to the Old Red System? Quartz rock, in all its 
various modifications, from a purely mechanical to-a purely 
crystalline stone, is of common occurrence in what are known 
as the primary districts; a bed of mica-schist is not unfre- 
quently found to pass almost imperceptibly, by gradually 
dropping its mica, into a true quartz rock; nor are such tran- 
sitions unfrequent in gneiss deposits; but the only true Red 
Sandstone I ever yet met in a so-called primary district is the 
Red Sandstone of the north-western coast of Scotland. It 
must represent, with the overlying quartzose and calcareous 
beds, an enormously extended period. Where, among the pri- 
mary rocks of the southern Highlands, for instance, or of any 
other region, shall we look for the deposits representative of 
the same age? Regarded as primary, it forms an intercalated 
period in the geologic history of this north-western tract of 
country, which we find unrepresented in every other district. 
I may add, that the quartz-rock formation, which runs diago- 
nally athwart the kingdom in detached patches, from Islay on 
the west to Banff and Aberdeen shires on the east, and which 
holds geologically a middle position between the gneiss and the 
mica-schist, is an altogether different deposit from the quartz- 
rock of Assynt. 
Both Dr. M’Culloch and the late Mr. Cunningham of Edin- 
burgh have stated, that a great formation of gneiss in the 
