In North Wales there are several valleys which run parallel or nearly parallel to the valley of the Bala fault, and, like it, are crossed by watersheds which are quite inconspicuous. One of these watersheds separates the head of Cwm Prysor from the source of Afon Tryweryn; a second parts the springs of the Conway from those of Afon Dwyryd; and a third divides the waters of Nant Ffrancon from those of Afon Llugwy (a tributary of the Conway). (Pl. XI.)

A short time since Mr. G. Trubenbach, Managing Director of the Newlands Diamond Mine, West Griqualand, drew my attention to a notice by Professor Beck of the paper which I read to the Royal Society last June, on the Parent-rock of the Diamond in South Africa, kindly sending me a translation of the original. As Professor Beck's criticisms are founded on such a travesty of my published opinions that I can only suppose his knowledge of our language to be very imperfect, and as the hypothesis which he advances appears to me untenable, I ask permission to reply to the one and point out the improbability of the other.

My attention has been directed to the following paragraph, which appears in Mr. H. B. Woodward's monograph on the Jurassic Rocks of Britain, vol. iii, p. 31 (1893). It is as follows:—

“Prof. Sollas has suggested that rivers sometimes bear to the sea considerable quantities of undissolved calcareous matter, derived from the formation through which they flow. This is a matter that requires confirmation, for it is known that carbonate of lime is more readily soluble in fresh-water than in sea-water.”

In 1877 Dr. Woodward recorded nineteen British species of the genus Conocoryphe, of which seven were doubtful. The following is the list of them:—

In connection with the revision of the Silurian area in Ireland, at present in progress by the staff of the Irish branch of the Geological Survey, a number of rock-specimens of the dykes occurring on the coast of Co. Down were lately petrographically examined by the writer, who detected in one of the slices a blue amphibole of secondary origin. As a mineral of this kind was not hitherto known to occur in sitû in Ireland, it may be of interest to put its discovery on record here and to give also a few details respecting its characteristics.

This species was first described by Sir P. De M. Grey Egerton as Palæoniscus monensis, in 1850, from detached scales from the Coal-measures of Anglesey. Subsequently, Dr. R. H. Traquair proved that the proper position of the fish was in his genus Rhadinichthys. Up to this date only detached scales had been known, but in the paper just mentioned Dr. Traquair described specimens showing many points in the structure of the fish which had been hitherto unknown. In my collection there are many fragmentary remains, collected from the Yorkshire Coal-measures, which show, among other interesting points, the form and ornamentation of many of the bones of the head and shoulder-girdle; while one more nearly perfect specimen shows well the form of the fish and some other points in its anatomy which have not been hitherto described, namely, the relative positions of the dorsal, anal, and ventral fins, the former being very well preserved and perfect.

In May, 1897, a fossil tortoise was found about 10 feet above low water-mark opposite Shepherd's Chine, by Mr. Wm. White, of Atherfield, Isle of Wight. It came into my possession in July of last year (1899). At that time the only portions clear of matrix were the sixth, seventh, and eighth costal bones, the edges of the marginals, and the epi- and hyoplastrals nearly to the notch ; the matrix is a fine silt containing much iron. The specimen had been subjected to long attrition by the sea. A very thin but hard seam of whole and broken Paludina had offered a stubborn resistance, as likewise it did against a finely pointed and tempered chisel. On the surface of the carapace are several Cyprids (sp. ?) and the impression in section of Paludina.

In a former number of this Magazine, and also in a Report published by the Geological Survey of Canada, I showed reasons for believing that while the land around Hudson Bay, in the northern part of Canada, had undoubtedly risen several hundred feet in Post-Glacial times, it has now reached a condition of stability similar to that of the land along the Gulf of St. Lawrence and on the eastern seaboard of Canada.

Ars longa, vita brevis. This is especially true when one reaches the age of 64. I therefore commit to paper some of the results of a geological investigation of Snowdon on which I am engaged. I start of course from the work of Messrs. Ramsay and Selwyn embodied in the Geological Survey Map of Snowdon and Ramsay's memoir on North Wales. To make what I have to say clear I may state that the rocks of Snowdon are by Ramsay and Selwyn divided into three principal groups, viz.: A, an upper felsitic lava ; an intermediate band (B) of bedded fossiliferous rocks of Bala age, containing much volcanic material, called the calcareo-felspathic ashy series ; and a lower mass (C) of felsitic rocks. This lower mass is in some places divided by sedimentary bands consisting of slates and grits. Below C come blue slates and grits, with occasional volcanic bands, D; and below D the great mass of volcanic rocks (E) which form Glyder Fach and Y Tryfan.

Recent studies about the average chemical composition of larger numbers of igneous rocks in the aggregate have shown that figures obtained from any one hundred or more samples are very similar, in fact practically equal. (See A. Harker, “On the Average Composition of British Igneous Rocks”: Geol. Mag., No. V, May, 1899.) This will be found also the case when comparing the following average which I calculated from the analysis of igneous rocks compiled by Roth in his “Petrographie der plutonischen Gesteine.”