Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/436

326 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 9, reason why the largest nugget lately found weighs only 2 oz. 17 dwts., if we suppose that the gold discoverable without washing or other modern appliances had been picked up by the prehistoric people.

Discussion.

Prof. Ramsay regarded it as certain that no quantity of gold would ever be found in purely glacial deposits, as in such detritus specific gravity went for nothing; but when those deposits came to be sorted by water, the gold became apparent, as in this case. He agreed with the author in regarding the granites in Kil-Donnan burn as metamorphic rather than intrusive, and had long held this opinion. The felspathic dykes were probably due to other causes.

Mr. D. Forbes, on the contrary, regarded the granite as eruptive, and accounted for the granitic veins following the lines of stratification, inasmuch as those were the lines of least resistance. The smaller interstices caused by the intrusion of the granite would be filled with quartz-veins derived from the granite, both probably containing gold. He considered that the gold had not been derived from Silurian rocks, but from the intruded granite or from the quartz-veins.

The Author was inclined to regard the granite in some instances as intrusive, and in others as metamorphic.

2. Observations on the "Nuggetty Reef," Mount-Tarrangower Gold-field. By Dr. George H. F. Ulrich, F.G.S.

The Mount-Tarrangower Gold-field lies about eighty-five miles due N.W. of Melbourne, at a mean elevation of 1200 feet above the level of the sea. Mount Tarrangower, from which the field derives its name, is a fine, massive, symmetrical hill, 1844 feet above the level of the sea by barometric measurement, thus rising several hundred feet above the level of the surrounding hilly country, and forming a conspicuous landmark for a great distance round. It and its eastern, northern, and southern spurs consist mainly of bluish-grey, hard, metamorphic Lower-Silurian Sandstone ("Hornfels") which crops out in beds, generally thick, but much cleaved, showing a mean strike of N. 12° W., and an easterly dip of 70°-80°.

About 500 feet down the rather steep western slope of the mount we meet the boundary of the extensive granitic tract, here generally known as "Bryant's Ranges," but forming part of the large horseshoe-shaped mass of which Mount Alexander, near Castlemaine, forms the highest point at an elevation of about 2800 feet. All along this boundary, which runs nearly due N. and S. for above six miles, numerous ramifications of the granite into the metamorphic rock can be observed, and there are also several small patches (inliers) of Silurian rock cropping out of the granite, which show in places round their boundaries an evident gradual passage into dark, fine-grained, micaceous, sometimes gneissose granite. It is singular that the strike and bedding of these Silurian inliers appear to be in no way disturbed or to deviate from those the rock shows beyond the