426 . PROFESSOR GEIKIE ON THE 
There need be little hesitation in placing the sandstones, shales, and 
conglomerates of Rhynie on the same horizon with those of Gamrie, Turriff, 
and the Spey. ‘Their position in Strathbogie, so far south from the main mass 
of Old Red Sandstone, shows over how much wider an area that system of 
deposits once extended than it now covers, stretching, as in this case, far up — 
one of the valleys among the uplands of Aberdeenshire. 
But a still more remarkable proof of the prolongation of the Old Red Sand- 
stone into ancient valleys or hollows, even in the heart of the Highlands, is 
furnished by another outlier which, as was shown many years ago by Hay 
CUNNINGHAM,* occupies a part of the valley of the Avon, near Tomintoul., 
Ascending Strathdon from the sandstone tract of Rhynie and Kildrummie, we 
find ourselves at last on the spurs of the Cairngorm Mountains, and, crossing 
the watershed, we look down upon the wild valley of the Avon, which rises at 
the base of the loftiest summits in the Grampian range. Granite, quartz-rock, 
gneiss, mica-schist, clay-slate, and other metamorphic rocks form these high 
grounds. It is not without surprise that following the Avon down its course, 
we suddenly come upon some deep ravines near Tomintoul, which the river | 
and its tributaries have excavated in a coarse conglomerate. In this case, as | 
at Rhynie, the deposit occurs as a long narrow strip, doubtless still represent- | 
ing approximately the position and trend of the ancient valley in which it was | 
laid down. ‘That former valley, perhaps occupied by the palzeozoic predecessor | 
of the modern Avon, ran in a north-north-easterly direction from the Avon to | 
-Glen Livet, a distance of rather more than seven miles, across the lines now | 
trenched by the Conglass and Chabet Waters. The ground on either side still | 
slopes up to heights of from 250 to nearly 800 feet above the platform of con- | 
glomerate. At the upper end, the conglomerate reaches a height of 1300 feet 
above the sea, but its northern or lower extremity is not more than about 800 | 
feet. * 
At several places the unconformable junction of the Old Red Sandstone o 
this outlier upon the crystalline rocks of the Highlands can be seen. Thus on | 
the Livet Water above Tomnavoulin a coarse conglomerate, with well-rounded 
blocks of metamorphic rocks, rests upon the reddened edges of the schists and | 
quartz-rocks. But the best sections in the whole basin are those of the Avon | 
and its tributary, the Water of Ailnack. Behind the village of Tomintoul the 
valley of the Avon contracts, and the river and its tributaries flow in magnificent | 
gorges sometimes more than 200 feet deep. These picturesque features have 
been excavated out of a crumbling red, green and grey conglomerate of exceed- 
ing coarseness. There is perhaps no other conglomerate in the north of Scot-| 
land so coarse and so tumultuous in its arrangement. Blocks six feet long are 
not uncommon, The mass, however, is a conglomerate and not a breccia, for| 
* “ Trans,, High. Soc.” vol. vii, 

