294 Proceedings of the Royal Physical Society. 
that where it is covered by the Upper Old Red the relation- 
ship between the two is that of a strong unconformability. 
Caledonian Old Red.—To the south of the Grampians, and 
perhaps also to the west, occurs another area of Old Red of 
considerable interest and importance. These rocks are in 
the main also of inland lake origin, and they include as well 
an important group of eruptive rocks. Sir Archibald Geikie, 
in his important memoir “On the Old Red Sandstone of 
Western Europe” above referred to, regards the greater part 
of these as having been deposited in a lake separate from 
Lake Orcadie, and for which he has proposed the name Lake 
Caledonia. I have found it very convenient, in describing 
these rocks, to convert this name into an adjective, and to 
speak of the rocks in question as the Caledonian Old Red. 
The precise stratigraphical relations of the Caledonian Old 
Red to the Orcadian cannot be made out by field-evidence 
alone. But the fish fauna of the Caledonian Old Red, Dr 
Traquair informs us, is of a decidedly older type than that of 
the Orcadian —and this appears to be the case even where 
fish from strata high up in the Caledonians are compared 
with the fish from the lower horizon of the Orcadians, as if 
the Orcadians, as a whole, were newer than the Caledonian 
Old Red. In the present connection this question is one of 
considerable importance, for if the two are of different ages, 
it is quite clear that one must have been formed before the 
other, and we have to take the sum total of the time required 
for the formation of both. 
Lanarkian Old Red.—In the Pentland area the Upper 
Old Red lies with a strong unconformity across the Cale- 
donian Old Red Rocks, which form the mass of the Pentlands, 
while these, in their turn, lie with a violent unconformity 
upon yet another series of Red Sandstones, whose close con- 
nection with the true Silurian rocks was clearly pointed out 
by Sir Archibald Geikie as far back as 1860 (Quart. Jour. 
Geol. Soc., xvi., p. 312). The interrelations of the three Old 
Reds in the Pentland area are admirably summed up by the 
same author in “ Siluria,” 4th ed. (1867), p. 250, in these 
words: “It thus appears that, between the Grampians and 
the Cheviot Hills, what has been called ‘Old Red Sandstone’ 
