In his article on septarian structure in the March number of the GEOLOGICAL MAGAZINE Dr. A. Morley Davies seems to call for further light upon the subject, hence the following is offered. The writer became convinced of the fallacy of the current teaching concerning the formation of concretions with cracked interiors and of septaria more than thirty years ago, and has so taught in his classes ever since. In 1902 he published a paper on “Concretions and their Geological Effects”, which presented facts which virtually demonstrate that the cracking is due to the expansion of the exterior rather than by a contraction of the interior, as Dr. Davies has also concluded.

During a short holiday to North Wales in Whit-week, 1910, I was investigating the igneous rocks to the south of Llanfairfechan, more particularly the intrusive greenstones of the Geological Survey map. Since the publication of this map, over fifty years ago, several districts within it have been investigated in greater detail, especially as to the volcanic rocks, but much remains to be done petrographically. One of these greenstones turned out to be of exceptional interest, being of a type of rock hitherto, I believe, unrecorded in North Wales, so another visit was made to it in August, 1912.

In the March Number of this Magazine Mr. Cowper Reed recorded the interesting discovery of a series of fossils which points to a Bartonian horizon for the Hengistbury ironstone. Upon reading this paper I was reminded of some chocolate-coloured clays with Foraminifera which I had collected from a seam between the ironstone bands at Hengistbury Head in August, 1895. The washings from these clays afforded abundant tests of arenaceous forms; and since, so far as I am aware, no Foraminifera have yet been recorded from this locality, it may be of some interest to publish the results of an examination of the material collected.

The very interesting remarks made by Messrs. Dewey and Flett on “Some British Pillow-lavas and the Rocks associated with them” have further emphasized Dr. Teall's observation of the intimate association of Radiolarian rocks with lavas of this character, and which is particularly well developed in Europe in the later Devonian formations. It is further shown that such rocks are characteristic of areas of continuous off-shore subsidence, and are often intimately associated with intrusions of dolerite, quartz dolerite, gabbro, and serpentine.

On looking over a miscellaneous collection of animal bones from a cave in North Wales, sent to me for identification by Mr. John H. Morris, of West Bromwich, I was pleased to discover the remains of the lynx, and as our knowledge of the occurrences of this animal in the British Isles is so scanty, it seems to me to be of some interest to record the present discovery.

The Riebeckite-Orthophyre of the Holy Isle.—Four Occuxrences of acid and sub-acid igneous rocks containing the rare soda-amphibole riebeckite have been recognized in Great Britain, of which that of Ailsa Craig is the best known. The occurrences of Ailsa Craig and Mynydd Mawr, Carnarvonshire, are riebeckite-microgranites or paisanites. They contain ragged moss-like areas of riebeckite, together with microphenocrysts of quartz and alkalifelspar, in a microcrystalline groundmass of quartz and felspar. Riebeckite was also found by Dr. Teall in the granophyre of Meall Dearg and the neighbouring area of Druim an Eidhne, Skye. Harker described the riebeckite in these rocks as occurring in two forms, one having the usual ragged, sponge-like appearance, and the other being idiomorphic, the faces in the prism zone being well-defined, but with irregular terminations. The fourth occurrence differs somewhat from the others. This rock occurs as an intrusion into the Upper Old Red Sandstone, or Calciferous Sandstone of Easter Eildon Hill, Melrose, and was described by Barron as riebeckite-trachyte or phonolite. It consists principally of sanidine, occurring both as microphenocrysts and in the groundmass, with interstitial patches of riebeckite, and a little nepheline. Harker describes the rock as an orthophyre.

Probably most teachers of petrology have experienced difficulty in making clear to some elementary students the manner in which light is transmitted through a polarizing microscope, and the explanation of birefringence and pleochroism. In such circumstances I have found very helpful the analogies illustrated by an easily constructed model. Doubtless such an instrument has been used before, but, as the textbooks make no mention of it, a description may be of use here.

In the Peterborough, Advertiser for December 16, 1911, there appeared an illustrated article on a “recent discovery” of a silted-up pre-glacial river-valley, 250 yards wide, at Fletton, near Peterborough. Eliminating from that article a good deal of scientific romance, there remains a certain residuum of geological facts, so far as the determination of them by the writer of this note has been carried out, through the courtesy of Mr. A. Adams, the Manager of the London Brick Company's works.

The Dane Hill Sandstone Group, as we propose to distinguish the higher of the two series of Upper Keuper sandstones, since it is well developed in the neighbourhood of the Dane Hills at Leicester, is well exposed in a little quarry at Ashleigh House. Here the highest part of the series is seen, with thin beds of flaggy marl and calcareous White or Green Marl, overlying a series of thick-bedded, currentbedded sandstones, of white colour, loose and friable, but hardening on exposure. The section has been described by Browne (1893), but at present is exposed to show a better sequence (see next page).

The Upper Trias of Leicestershire as a whole occupies the western half of the county, being bounded on the east more or less by the Soar Valley, following the strike (as a subsequent in part of its course up to its junction with the Wreake). In fact, it is on the eastern boundary near the outcrop that the beds are mainly best exposed, the region to the west south of the coal-field around which it mantles being little developed and presenting fewer exposures.

For some time past I have had a difficulty in understanding how certain striated flints from various horizons stood, without breaking, the pressure to which they must have been subjected when such markings were imposed upon them. This difficulty increased when I found that thin flakes from the present land surface exhibited well-marked striæ, and as experiments with my presses had shown that even large flints will break up under no very great pressure, the possibility occurred to me of these scratches having altered since the flints were first subjected to the scratching process. I reasoned that if a point passed over a flint under pressure the area upon which the point impinged would be shattered, and that small plates or splinters of flint would be formed along the line of movement. I also concluded that, as with the thin plates which are produced on a flint when flaking, and which are not found upon implements which have been exposed to atmospheric conditions, these fragments would in time, by thermal effects, ‘weather out’ and leave a clean-cut groove behind.

Bathymetric surveys have revealed much that is very interesting concerning the ocean floors, not only as regards the deeper portions, but also as concerns the continental shelves. Hull has constructed charts of the North Atlantic and shown that many of the shallower areas are of such a form as to suggest that they were originally portions of existing river-basins, and that the submerged valleys may be traced along the sea bottoms to depths of more than a thousand feet round the present continents. Similar submerged troughs have also been noted along the margin of the Asiatic continent. Two such well-marked channels occur in the ocean at the mouths of the Indus and Ganges. Indeed, the phenomenon would seem to be one common to all the continental shelves.