Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/433

1869.] JOASS-SUTHERLAND GOLD-FIELD. 323 pound of felspar and quartz (c), commonly interbedded with, but once apparently intersecting, the strata.

The more felspathic varieties of this granitoid rock are readily disintegrated, forming either a white plastic clay or a gritty siliceous sand, according to the predominance respectively of felspar or quartz. Towards the head of the stream, this and other granitiform rocks, large-grained, pinkish, and friable, become abundant, forming great slopes of granular grit, from which the locality at the Suisgill forks takes its Celtic name of Feithegaineamhaich, or the Sandy Swamp. The same name, and for a similar reason, is given to the head of one of the streams running into the Langwell Water, in the neighbouring district of Caithness.

In the small stream Allt-an-t'fhionnaraidh, to the south-east of Suisgill, a water-rolled pellet, about 1/2 inch in diameter, and containing gold in intimate connexion with felspar and quartz, was recently picked up without washing. So far as the origin of the gold may be inferred from such a small specimen, it suggests the binary granitiform layers and grits of the upper Suisgill.

In Kil-Donnan burn, where, as is now generally known, the Sutherland gold was first discovered by Mr. R. N. Gilchrist, a native of the county, on his return after a seventeen years' residence in Australia, the flaggy rocks are generally quartzose and gneissose, dipping E. and E.S.E., with an occasional veer to the N.E. Quartz-veins of small size occur here, generally encased in chloritic clay. The felspathic rock c is also present, but not in abundance. The drift, which at its contact with the bottom rock, sometimes consists of bluish and yellow clay with light-coloured patches, is most frequently, as in Suisgill, a ferruginous gravel with rolled boulders, apparently of local origin. Above occurs yellowish clay, overlain by coarse sand, containing dark flexed earthy lines in section, the whole covered by thin peat moss. Gold is found in the greatest quantity in the lowest portion of the alluvium, but is obtained occasionally from wash-dirt immediately under the surface turf (fig. 4).

In the streams which run into the Ullie from the N.E., between Kil-Donnan and Kil-Pheadar (namely Allt-duible, or the double burn, which runs into one before reaching the river, Allt-bhreacaich, the speckled burn, from the quantity of quartz lying about its slopes, and Allt-torrish, the burn of mounds, from its numerous prehistoric tumuli), the rocks preserve the same character and general easterly dip, with some slight local variations. All these streams are auriferous, but not richly so. Kil-Pheadar and Caien burns traverse the granite of the Ord; and no gold has been discovered in them, although their nearness to Helmsdale village, where many of the miners lodge, prompted and facilitated careful and frequent search.

The same persistence of easterly dip is traceable as we cross the strike to the Old Red Sandstone at Berriedale, on the Caithness coast. The rocks, however, become more quartzose till they pass upwards into the quartzite mountains of the Sgerreabeinn range. The occurrence of these quartzites, and the fact that prospecting was prohibited within the Berriedale district, probably occasioned