The late eminent palæontologist, Mr. Salter, F.G.S., characterized the portion of the lovely valley of the Mawddach, at, and near the Falls of the Cain and Mawddach Rivers, "a perfect geological puzzle."

Certain it is, that touching Tyddyngwladus, the survey maps are greatly at fault; and, that the rocks, thereabouts, most of them, are of precambrian age.

Dr. Hicks, F.G.S., has hit upon the truth, approximately, I think, in what he calls Dimetian at St. David's, (as applied to the lowest beds of this district.)

After more than a year's unceasing investigation of these puzzling rocks and their associated minerals (chiefly with reference to the modes of occurrence of the "precious metals").

The blue substance first came under my observation many years ago in one of the Slickensides, in the first quarry opened for the supply of Abriachan granite, and situated by the side of the road leading to Abriachan,-a somewhat isolated district amongst the hills overlooking Lock Ness.

It was then seen in purplish-blue spots, dotting here and there the surface of the rocks which had been exposed to considerable weathering, and over which water had poured freely.

Dr. Haughton, by his numerous analyses of the black mica of the Irish granites, may be said to have established the specific individuality of the lepidomelane of Hausmann.

That mineral his analyses showed to differ from Biotite in its great excess of ferric oxide and its comparative deficiency of ferrous oxide and magnesia.

Some time since Prof. Ruskin kindly sent me a specimen of goldquartz brought from New Zealand by Mr. H. A. Severn, giving me leave to cut thin slices for the microscope, and asking me to examine the same. The result seems to me of some interest, and Mr. Ruskin has kindly consented to my bringing it before the Mineralogical Society, together with a notice of a strangely beautiful gold occurrence, described by Mr. Severn as disclosed by blasting in one of the New Zealand gold reefs.

Since my former communication to the Mineralogical Society I have been endeavouring to obtain a sufficient quantity of the pure mineral therein described to complete my analyses. Plenty of what certain dealers have been selling as Penwithite is obtainable from the rubbish heaps at Wheal Owles, but this is mostly dark-brown—nearly or quite opaque, pitch—like in appearance, and of very variable composition-the silica alone varying from 22 up to 57 p. c., and the sp. gr. often being as high as 3.4.

The true mineral is sometimes attached to masses of such material—it is highly vitreous and transparent, from dark amber to reddish-brown in colour, H. 3.5 and sp. gr. only 2.49—a remarkable circumstance considering the large amount of manganous oxide present.

About a year since I received from our associate Mr. Alfred Davies, of St. Agnes, a dark-brown mineral which was supposed to consist largely of sulphide of tin. As it differed greatly in appearance from the socalled tin pyrites, I at once felt interested in the supposed new mineral, and commenced an analysis which I have lately been able to complete.

It is generally granular in appearance, dark-brown, translucent very slightly on thin edges, infusible B.B,, soluble more or less completely in aqua regia, &c.—in fact its properties differ but little from those of an ordinary dark variety of blende, except that with careful manipulation it yields a bead of tin when treated with reducing agents on charcoal.

It is only within the last century that the Cingalese have become the most astute judges upon all matters relating to gems in their uncut or natural state. That this is so is proved by the number of remarkable stones which previously found their way to England, unrecognized as being of any value; amongst them is the stone in question. How it could have been passed over and treated by the merchants as of no value is a mystery, unless its great size contradicted the probability of its being a gem. Such, however, was the case ; it having been sent to England mixed with the ordinary pieces of inferior Rubies and Sapphires used by watchmakers. It was sold for a mere nominal sum, as a piece of Quartz, or Crystal, and passed into a private collection of minerals, the owner of which regarded it also as a specimen of Quartz.

During the last three years I have been engaged in collecting and cataloguing the minerals of Japan. The following is a list of the species with which I am acquainted. The arrangement is according to the classification given by Dana in his System of Mineralogy.