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Nature volume 13, pages 439440 | Download Citation

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Geological Society, March 8.-Pro. P. Martin Duncan, F.R. S., president, in the chair. -W. J. Chetwood Crawley, Walter Keeping, Joseph Thompson, and William W'alker, were elected Fellows of the Society. The following communications were read:-I. On the influence of various substances in accelerating the precipitation of clay suspended in water, by Mr. Wm. Ramsay Principal Assistant in Glasgow University Laboratory. Communicated by Prof. Ramsay, F.R.S., V.P.G.S. The author referring to the fact that clay when suspended in water in excessively minute particles, settles more rapidly when the water contains salts in solution, noticed the opinions expressed by previous writers on the subject, and gave the results of experiments made by him, from which it would appear that the rapidity of precipitation is proportionate to the amount of heat absorbed by the salts in process of solution. By another series of experiments he found that the fluidity of the respective solutions had apparently no influence on the rapidity of deposition of the clay. He also found that clay is deposited less quickly in acid solutions than in solutions of salts, and more rapidly in a solution of caustic soda than in one of caustic potash. In solutions of common salt of different strengths he found that clay settled in the inverse order of their specific gravities. From all these results the author is inclined to attribute the varying rapidity of the settling of clay suspended in saline solutions to the varying absorption of heat by the solutions. When water containing suspended clay was heated, the rapidity of the settling of the clay was proportionate to the heat of the water. The author suggests that the increased rapidity of settlement may be due to the greater amplitude of vibration of the molecules of water when heated; the vibrations being performed in equal times, particles descending at right angles to the plane of vibration will experience less resistance from the molecules of water. A note by Prof. Ramsay, briefly indicating some of the geological bearings of these results, was appended to the paper.-2. On some Fossiliferous Cambrian Shales near Carnarvon. By Mr. J. E. Marr. Communicated by Prof. T. McKenny Hughes, F.G.S. With an Appendix, by Mr. Henry Hicks. Tl e shales described by the author extend from about three miles S.W. of Carnarvon to Bangor, running nearly parallel to the Menai Straits. They are faulted against Lower Cambrian to the east, and disappear against a dyke on the west. The shales vary from greyish black to bluish black in colour, and are generally sandy and micaceous, but in places chiefly clayey. Fossils were obtained from three places on the banks of the Seiont, namely, near Point Seiont (where the beds are concretionary in structure), along the old tramway from Carnarvon to Wanttle, and near Peblig Bridge. The first-named locality is richest in fossils; and here there is a greenstone dyke, parallel to the bedding of the rock, and altering the shales for a distance of about four yards from the edge of the dyke. The fossils seem to indicate that the deposit belongs to the upper part of the Arenig group. Mr. Hicks pointed out that the fauna clearly showed that these beds belong to the Arieng group, many of the species being identical with those found in the upper part of that group at St. David's Shelve, and in Cumberland. The new species found by Mr. Marr are a Caryocaris (C. Marrii) and an Eglina (A. Huilhesii). The other fossils were Didymo-graptus indenlus, D. bifidus, D. Murchisoni, and the var. furcil-latus. Species of Barrandea, Trinuclcus, Lingula, Obolella Ducina, &c., and Orthcceras caeresiense. The rock in its general character is extremely like that at the same horizon in the succession at St. David's Shelve, and hi Cumberland, and indicates, therefore, the prevalence of similar physical conditions when deposited. The rock is such as would be formed over an even sea-bottom at some considerable distance from land and in moderate deep water. Mr. Hicks looked upon this discovery as of considerable importance, since it clearly proved the position of beds hitherto imperfectly known, and moreover shows that similar conditions prevailed over extensive areas at the time these beds were deposited. It also furnished further evidence in support of Mr. Hicks's opinion that no break occurs anywhere in the Welsh area between the Cambrian and Lower Silurian rocks. _3. On the occurrence of the Rhictic Beds near Leicester. By Mr. W. J. Harrison, Curator of the Town Museum, Leicester. The sections described by the author are shown in brick-pits in the Spinney Hills, forming the eastern boundary of the town of Leicester, and in the Crown Hill on the eastern side of a valley excavated by the Willow Brook. In the latter locality they are capped by Lower Lias. They have a slight dip to the south-east.

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https://doi.org/10.1038/013439a0

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