601 
of Edinburgh, Session 1877 - 78 . 
The south-western and southern margin of this great northern 
basin of the Old Red Sandstone can still he traced nearly continu- 
ously from the confines of Caithness to the borders of Aberdeen- 
shire, its position being marked by a zone of littoral conglomerates. 
Beyond the edge of that zone, however, there occur some interesting 
outliers, which in some cases may represent long fjord-like indenta- 
tions of the coast-line ; in others may mark what were really inde- 
pendent basins lying at the base of the Grampian mountains. The 
author points out that probably most of the difficulty which has 
hitherto been experienced in understanding the sequence of beds 
along the southern shores of the Moray Firth, and their parallelism 
with those of Caithness and Orkney, is not to be attributed to the 
amount of detritus covering the country, but rather to the fact which 
has not heretofore been observed, that the Upper Old Red Sand- 
stone, with Holopty chius and Pterichthys major , really overlaps 
unconformably upon the older nodular clays and conglomerates with 
Coccosteus, Cheirolepis , &c. This relation can be satisfactorily 
determined in Morayshire, and is now being worked out by Mr 
John Horne in the course of the Geological Survey. The author 
traces in great detail, from the Spey into Sutherlandshire, the 
development of the lower sandstones, conglomerates, and clays, which 
have been regarded as equivalents of the Caithness flagstones. He 
thinks that in no sense can this comparatively thin group of rocks 
(seldom 1400 feet in depth) be regarded as a mere southward 
attenuation of the great Caithness series, as suggested by Murchison, 
for that neither lithologically nor palseontologically can that view be 
sustained. He has been led to the conclusion that the whole of these 
rocks from the borders of Sutherlandshire to those of Aberdeenshire 
represent only the higher portions of the great Caithness series, and 
that they were formed during a gradual depression of the ancient 
high grounds whereby the waters of Lake Orcadie were allowed to 
creep southward over the descending land. This movement is indi- 
cated by the character of the strata, and that it took place about the 
time of deposit of the later flagstones of Caithness is shown by the 
occurrence of the fossils of that division in the nodules, flags, and 
clays of the Moray Firth region, while those of the Lower division 
are absent. 
Allusion is likewise made to the discovery of two localities where 
