Vice-President’s Address. 293 
Unconformity at the Base of the Upper Old Red.—In the 
English Lake District the Upper Old Red lies across, or 
oversteps, the ends of strata fully as much as five miles in 
thickness.!_ In Scotland it lies unconformably across all the 
strata older than itself. At the Old Man of Hoy, for example, 
the Upper Old Red forming the “Old Man” lies in a nearly 
horizontal position on the ends of beds very high up in the 
Orcadians, which are tilted, Dr Heddle tells me, at angles of 
30° to 35°. Within a short distance the same Upper Old 
_ Red oversteps fully 7000 feet of the Orcadian Rocks there. 
I very strongly suspect, as already hinted above when dis- 
cussing the New Red, that this same unconformity of the 
Upper Old Red upon the older rocks will be found, on closer 
examination, to extend into the areas occupied by the 
Devonian Rocks of Cornwall and Devon as well. In Scot- 
land, as already noticed, it lies across not only the Orcadians, 
but across every member of the Caledonian Old Red in Perth 
and Forfar, and also in the Pentlands. In Ireland the same 
striking fact has been described by many observers. For 
reasons given below, however, I am disposed to leave this 
unconformity out of account. 
Orcadian Old Red.—The Old Red Sandstone rocks of the 
Moray Firth, Caithness, Orkney, Shetland, and some other 
areas in the north-east of Scotland, are regarded by Sir 
Archibald Geikie as having been laid down in a different 
basin of deposit from those south of the Grampians. He has 
proposed for this basin the name of Lake Orcadie, a name 
which has suggested to other geologists the very suitable 
adjective Orcadian, which of late years has been much used 
in referring to these rocks. The Orcadians consist of a vast 
thickness, possibly many thousands of feet, of strata, which 
in the main have evidently been very quietly and slowly laid 
down in an area of inland drainage. Dr Traquair’s researches 
upon the fish fauna render it certain that the formation 
of these rocks must have occupied a very long interval 
of time. To the consideration of this formation we shall 
return presently. It will suffice to repeat the statement here, 
1 Silurian Rocks, 14,000 feet; Coniston Limestone and Borradale Volcanic 
Series, 12,000; Skidda Slates, 12,000+. 
