1869.] JOASS — SUTHERLAND GOLD-FIELD. 317
more and more gneissic in character, and, perforated as they are
at intervals by granitic and porphyritic rocks, have, in all probability,
afforded the auriferous detritus of Eastern Sutherland. These
rocks, which formerly were not separated from the old or fundamental
gneiss, though they have the true Silurian strike from S.W.
to N.E. (which is rectangular to the strike of the Laurentian rocks),
are in parts intensely metamorphosed, whether it be in the high
plateau south and west of Tounge, or where they roll over until
they reach the eastern slopes of Sutherland and Ross, having in
both localities been powerfully affected by eruptive rocks. Judging,
then, from the composition of these various rocks, and particularly
those described by Mr. Joass, we need not travel further westward
from these eastern slopes than to the great central plateau to look
for the origin of the gold-detritus; and when we examine the matrices
of the auriferous fragments we find that this inference is sustained
by their composition.
Finally, I am led to infer, from my acquaintance with the rock- formations of the North Highlands, that there is little chance of discovering in them any notable bodies of rock in situ charged with rich auriferous bands analogous to those which are associated with the Lower-Silurian slates and schists of Australia and California.
Notes on the Sutherland Gold-field. By the Rev. J. M. Joass.
It is proposed to arrange the following remarks as under : —
1. The extent of the gold-field as at present ascertained. 2. The general character of the prevailing rocks. 3. The associated rocks. 4. Detailed descriptions referring to map and sections. 5. Probable source of the gold. 6. General remarks.
1. The extent of country over which gold has been ascertained to occur in the south-east of Sutherland and contiguous portion of Caithness may be stated as measuring 30 miles from east to west, and about 20 from north to south. This is exclusive of several widely detached places in the north-west and south-west of the county, where small quantities of gold are credibly reported to have been found. A few points in the north of Caithness, and Unst, in Shetland, are held to be auriferous.
2. The prevailing rocks of the district are believed, on the authority of Sir R. I. Murchison, to belong to the Lower-Silurian series. This may be regarded as settled by his masterly analysis of the evidence for the intimate connexion of these rocks with large deposits on the north-west, which from their included fossils are admitted to belong to that system. Within the district referred to, these rocks occur as flaggy micaceous, gneissose, and quartzose strata, with a south-easterly dip. With a few local exceptions this dip is unaffected by the presence of numerous igneous rocks, whose
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