1869.] JOASS-SUTHERLAND GOLD-FIELD. 325
6. The material in which the granular gold occurs, namely the
detritus overlying the abraded edges of the flaggy Lower Silurian
rocks, may be partly of glacial origin, but is not necessarily far-
travelled, for its included boulders seem to be of local origin. It
has been arranged by water, but probably that of the streams near
which it lies and not that of the sea, judging from the unwashed
moraines which occur at lower levels in the valley of the Brora.
The extent of the auriferous country will probably be found to correspond with the range of the more highly metamorphosed Lower Silurian rocks; and since these may be found in more or less force as far as the northern coast of Sutherland, the area of the gold-field may yet, perhaps, be extended. Nearly every stream within the area here described has been well searched by practical diggers; and the fact that many of them, as already mentioned, have been searched in vain, suggests no wide-spread deposit, the result of extensive glaciation, but several independent centres connected with the local rocks.
The question of the continuance of gold-seeking as a source of remunerative labour must depend upon the extent to which these its parent rocks may be found to occur. This can only be ascertained by systematic prospecting, which will doubtless be encouraged when questions now pending between the agents of the Crown and those of the noble proprietor of the ground are satisfactorily settled.
Already the results have been a fair return for skilled labour, amounting to the value of about £3000, so far as I can ascertain by inquiry and careful calculation.
In conclusion, it may perhaps not be held irrelevant to remark that the Pictish Towers, a class of ancient buildings very numerous in Sutherland, are specially abundant within the ascertained auriferous district, and further appear, wherever they occur, from Shetland to the south of Inverness-shire, to be associated with rocks which may be more or less auriferous — namely the Lower Silurian, believed on very high authority to be the most frequent source of gold in all parts of the world.
These forts were apparently erected against maritime invaders. Their number and strength suggest the frequency and formidable nature of such invasions, for which a motive may be found in the supposition that south-eastern Sutherland and other districts where such duns or burgs occur were known in prehistoric times to be rich in gold or other mineral treasures. Hence, perhaps, the connexion between the copper of Sandness and Mousa-burg in Shetland, the lead and silver of Beaufort and Struidh-burg in Inverness, the gold of Durness and Dun-Dornadilla in West Sutherland, of Uisge-dubh and Caisteal-Coille, of Allt-Smeorail with Aschoille-burg on one side, and Coir-Aoiscaig tower on the other, and of Strath Ullie, with its chain of Pictish strongholds from Dun-uaine on the coast to the wonderful group of Cyclopean structures that crown Beinn-Ghriam-beg twenty-eight miles inland.
Hence, too, perhaps, the origin of the native torques and armillae of beaten gold, attractive booty no doubt to the roving Norse-men, "the exactors of rings;" and hence, also, it may be, one
