442 PROFESSOR GEIKIE ON THE 
found to include even the thin fibrous crust of calcite so characteristic at Gamrie 
and elsewhere. Though the actual junction of the Old Red Sandstone with 
the Highland rocks is here obscured, the two formations approach so nearly as 
to leave room for no more than a very thin band of conglomerate. Only two 
miles to the west, however, as appears by section vii, a mass of coarse con- | 
glomerate, about 400 feet thick intervenes between the position of the Knock- 
loan fish-bed and the base of the series. Spreading out over a space about 
two miles in breadth, this conglomerate forms the material out of which the 
gorge above Cawdor Castle has been excavated—a narrow picturesque gully 
often more than 130 feet deep, with tortuous convex and concave sides, which 
here and there approach within a few yards of each other at the top. Despite 
its rent-like aspect, it is a true case of brook-erosion, as is shown by the numerous 
segments of old pot-holes at many levels far above the present reach of the 
highest flood. The stones of the conglomerate are mostly water-worn, though 
more angular shapes appear among them. They consist of fragments of the 
gneiss, quartz-rock, granite, and other crystalline rocks of the district, the larger 
blocks, one foot or more in length, being often well-rounded. The stratification 
is shown partly by the position of the flatter stones and partly by the intercala- 
tion of occasional thin lenticular bands of dull purplish-red sandstone, the dip 
being so gentle towards the valley of the Nairn that it nearly coincides with the 
slope of the ground. Mr Horne infers, I think with much probability, that | 
this thick mass of conglomerate accumulated in a bay of the old coast-line of 
the lake. He finds that while it disappears so rapidly towards the north-east, it | 
quickly diminishes also in thickness in a south-westerly direction. About three 
miles to the south-west it is 250 feet thick. Near its base at Galcantray, a | 
thin lenticular band of cornstone occurs, in which fish-scales and bones may be | 
detected. The lowest strata consist of a breccia sometimes highly calcareous, | 
like those of Banffshire, sometimes made up entirely of broken débris of a pink | 
quartz-porphyry, on which it rests. Grey shales and clays about 30 feet | 
thick, with calcareous ichthyolitic nodules, no doubt the same band as that of | 
Knockloan, crop out near Cantray, about 250 feet above this lower cornstone 
band. Westward at Clava, apparently on the same horizon as these nodule- 
bearing clays, there occurs in the channel of the river Nairn a series of hard | 
grey-blue and reddish calcareous flagstones, shales, and impure limestone, | 
which, since Dr Matcotmson’s early observations, have been known to yield 
fish remains. I was struck by the resemblance of these strata to some parts of 
the true flagstone groups in Caithness. From the Nairn valley at this locality, 
northward across the Culloden or Drummossie Muir, to the low country skirt- 
ing the Moray Firth, occasional exposures of the strata are to be seen. Putting 
the available evidence together Mr Horne has compiled the vertical column v. 
This is only a provisional computation. It shows, however, what cannot 

