Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/656

474 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 27, strata and the Laurentian ; and I have succeeded in discovering in various places : —

1st. The unconformable contact of the Lower Silurian gold-bearing strata with the underlying gneissoid and schistose series.

2nd. The unconformable contact of this gneissoid and schistoid series with the old porphyritic gneiss which I had before described as Laurentian.

3rd. The unconformable contact of the gold-bearing series with the old Laurentian gneiss, showing the absence of the intermediate gneissoid series, or the Huronian.

These several points of contact are visible at both extremities of a patch of Huronian strata about four miles broad, overlying the Laurentian on the Windsor and Halifax Railway, commencing one mile, or thereabouts, south-east of new Stillwater station, and terminating at Uniacke's second lake, and more than half a mile west of Mount Uniacke station.

V. The Laurentian Series.

The rocks last described are visible, as already stated, in unconformable contact with a coarse porphyritic granitoid gneiss near Stillwater station. The strike of the granitoid gneiss is N. 10° W., dip W., at an angle of about 48°. Five miles further south, and within a third of a mile of Mount Uniacke station, the Silurian quartzites rest on the Laurentian gneiss, the quartzites having a strike N. 75° W., and the old gneiss N. 20° W. Between Stillwater and Mount Uniacke the Huronian series rests on the old gneiss, and the Silurian on the Huronian ; but north of Stillwater and south of Mount Uniacke the Silurian strata are in contact with Laurentian gneiss, and so continue until another patch of Huronian is reached, this last-named series appearing to cover comparatively small areas in the great Laurentian valley between Halifax and Windsor ; but in the more western counties it is exposed, I have reason to believe, to a very considerable extent.

In the county of Guysborough (fig. 4) the gold-bearing rocks at Sherbrooke rest on the Huronian, which, again, is seen close at hand in contact with the old Laurentian gneiss. In the middle and eastern part of Nova Scotia the thickness of the Huronian does not appear to be very considerable ; but no complete section has yet been crossed, except at Sherbrooke (fig. 5). Between Halifax and Windsor the Lower Silurian series occupies a great valley or synclinal fold in the old Laurentian gneiss. The average breadth of the valley is nine miles. Its general course is north-west (true) ; and the gold-districts of Mount Uniacke and Hammond's Plains are arranged on its western boundary — and those of Lawrencetown, Montagu, Waverley, and Renfrew on the eastern boundary of the valley, occupying crowns of anticlinals which have a general north-east-by-east direction (fig. 1).

In one part of the county of Guysborough the Laurentian, with a narrow band (as far as known) of Huronian, forms a nucleus, having