Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/364

306 Professor Thompson's analysis would agree well with the former portion of the microscopic determination ; but the soluble portion is rather difficult to understand, there being no appearance of a highly hydrated silicate in the rock.

Be this as it may, around Mount Wheeler, within a radius of a mile the serpentine is traversed by auriferous reefs, whilst the extension of the same band of serpentine over a large area beyond this contains no parallel to the auriferous area round the above-mentioned hill.

Some 30 yards from the bluff face of the Mount, the serpentine was found to contain gold sufficient in quantity to pay for mining to a depth of 20 feet below the surface ; gold was also found even to a depth of 80 feet, but not in remunerative quantities. This was known as "Block's Claim ;" and it affords additional ground for believing that the intrusion of Mount Wheeler was an active cause in the mineralization of the country around it.

In the Cape-River district, the influence of this class of felsite dykes is particularly marked : and it was whilst in the preparation of a detailed map of this gold-field that the practical value of these conditions was first realized by myself.

A plan of one of these dykes, which occupy the whole of Paddy's and Sharper's Gully, and cross Golden and Nuggety Gullies at their richest points, is here reproduced (Fig. 16) from the published map of the Cape Gold-field, in order to afford a crucial example of this mode of gold production.

At the intersection of this dyke with the quartzites and mica-slates of the metamorphic series, a fine example of a friction-breccia is seen on a steep hill- slope about one third of a mile from the junction of Paddy's Gully with the Running Creek, up to its junction with Golden Gully.

The gold found in Paddy and Sharper's Gullies was either in the form of losely aggregated fine gold, forming spongy nuggets, or very fine dust, the material adhering to which was a more or less decomposed form of the felsite.

The detritus of this formed the "wash-dirt," and the rock itself the " bottom," or " bed rock," of those miners who were fortunate enough to obtain claims in either of these rich gullies. Large patches of soil on the slopes leading to these watercourses, and on the watershed between Golden and Nuggety Gullies, were leased for "surfacing," the character of the gold and rock being the same in all these cases.