CHAPTER XXXVIII 
THE BASALT-PLATEAU OF THE PARISH OF SMALL ISLES RIVERS OF 
THE VOLCANIC PERIOD 
iii. PARISH OF SMALL ISLES PLATEAU 
The parish of Small Isles includes the islands of Eigg, Rum, Camia, Sanday 
and Muck (Map VI.). The fragmentary basalt-plateau which it contains, 
although the smallest of the whole series, is surpassed by none in the variety 
and interest of its geology. It contains by far the most complete records ot 
the rivers which, during the volcanic period, flowed across the lava plains. 
And it alone has preserved a relic of the latest lava which, after the 
basalt-plateau had been built up and had been greatly eroded, flowed over 
the denuded surface in streams of volcanic-glass that found their way into 
a river-channel and sealed it up. 
That the fragments of the basaltic plateau preserved in each member oi 
the group of the Small Isles were once connected as a continuous volcanic 
plain can hardly be doubted. Indeed, as already stated, they were not 
improbably united, with the plateau of Skye on the north, and with that 
of Mull, Morven and Ardnainurchan oh the south. Taking the whole 
space of land and sea within which the basalt of Small Isles is now 
confined, we may compute it at not much less than 200 square miles. In 
Eigg, Muck, Canna and Sanday the basalts retain their almost horizontal 
position, and from underneath them the Jurassic strata emerge in the 
first of these islands. The central part of the plateau in the island ol Rum 
has suffered greatly from denudation. It now consists of four small outliers 
of basalt, which lie at levels of 1200 feet and upwards, on the western 
slope. The basalt is underlain by a thick mass of red Torridon Sandstone, 
which, with some gneisses and schists, forms the general underlying platform 
of this island. These rocks are doubtless a continuation ol the red sand- 
stone and schists of Sleat, in Skye, and like them have been subjected to 
those post-Cambrian convolutions and metamorphism whereby the Lewisian 
Gneiss and Torridon Sandstone have been brought above younger rocks, and 
have been crushed and rolled out so as to assume a new schistose arrange- 
ment. Before' the time when volcanic action began, a mass of high ground, 
consisting of these ancient rocks, stood where the island ot Rum is now 
