Spheroidal Concretions Research Articles

On the occurrence of Cretaceous fossils in Caithness

In the paper published last year in the Society's Transactions “ On Egg-shaped Stones dredged from Wick Harbour,” the sand-pit at Leavad, situated twelve miles W.S.W. of Wick, was referred to. It was there noted that the sand and sandstone of this pit are unlike any rock of undoubted Old Red Sandstone age in the county, and the remarkable large spheroidal concretions were specially mentioned. It was the writer's opinion then that the rocks there are in situ and probably belonged to the Jurassic Formation, and that the very similar egg-shaped concretions which have been dredged from Wick Harbour were perhaps derived from a bed on the same geological horizon near Brora, and have been carried northwards as boulders to Wick, by ice, during the glacial period. The similarity of the rock and the shapes of the concretions at both places render this highly probable. This year Leavad was again visited and fossils were found in the sandstone in a poor state of preservation, but sufficiently good to determine the horizon of the deposit. This discovery makes a particular description of the sand-pit and its neighbourhood desirable, though it must be confessed that there is some doubt as to whether the rock is actually in situ or may be a glacially transported mass. Leavad sand-pit is situated in the valley of the Little River, a branch of the Thurso Eiver, which flows northwards and enters the sea at the town of Thurso, fourteen miles away. It is eleven miles west

III.—The Relation of the Concretionary Nodules of the Yarra to the Calcareous Nodules known as ‘Coal-Balls.’

Spheroidal concretions from the Yarra estuary which were to found to contain plant-remains were described by Mr. Chapman recently in this journal. The structures in themselves are of considerable interest to geologists, and also to palæobotanists from the fact that they contain “matted fragments of woody and foliaceous-material.” They were made the subject of some comparisons with the calcareous concretions from the Lancashire Coal-measures, and as a result certain general considerations were brought forward, which call for comment, and which are of sufficient importance to receive attention.

On the Porphyritic Rocks of the Island of Jersey

Having been supplied some years ago, through the kindness of my friend the Rev. C. Noury, of St. Helier, with a good series of specimens of porphyritic rocks from the Island of Jersey, I was struck by the exceptional appearance of some felsitic and globular varieties, in which the spheroidal concretions, instead of being minute globules, as in the usual pyromerides, attained a size of two feet and more in diameter. According to the information which I then possessed, the porphyritic rocks occupied the whole of the north-eastern part of the Island, resting on Cambrian schists, and underlying, from Rozel to St. Catherine's Bay, a coarse conglomerate, which had been described by Ansted as New Red Sandstone . At that time I strongly advocated the views entertained by my distinguished friend M. Michel-Lévy, on the relation between structure and geological age in eruptive rocks; and, judging from many examples collected in various districts of France, I believed that every felstone and pyromeride would be found to be of Permian age. Accordingly, as this belief seemed to be warranted by the facts in Jersey, I described the whole of the porphyritic rocks of the Island as Permian . Moreover, I even ventured to lecture my English predecessors for having failed to recognize the true age of the eruptive series, the felsites of Jersey having been described by Mr. Davies as “ old rhyolites .” This was a mistake on my part, which I now feel myself bound to confess before the Geological Society of

On the Spheroid-bearing Granite of Mullaghderg, Co. Donegal

On returning from a recent inspection of the field-work of the Geological Survey in Ireland, Prof. A. Geikie brought with him some remarkable specimens of spheroidal concretions, which, on account of their interesting structure, he thought worthy of detailed examination and description. For this purpose they were entrusted to me, and the present paper records my observations. These bodies were found by Mr. J. R. Kilroe, of the Geological Survey of Ireland, in granite at Mullaghderg, Dungloe, Co. Donegal. According to Mr. Kilroe, they occur in a mass, measurig 5 or 6 cubic yards, which lies in coarse granite. It consists “of concretionary balls, varying in size up to 6 inches in diameter. The balls are usually flattened and lie almost contiguously, the interstices being filled by granite, which is similar in character to, though muchfiner-grained than, that surrounding the entire mass.” In a letter I have since received from Mr. Kilroe he informs me that dykes are numerous in the locality where the spheroids occur. One of these passes quite close to the mass containing the concretions; but since the latter are confined to a small space and do not follow the dyke, I see no reason for connecting their formation with its intrusion. The Normal Granite.—Of the granite referred to above, Mr. Kilroe was kind enough to furnish me with specimens. It is a coarse-grained rock, varying in colour from a pale fleshtint to a reddish brown. The specimens in my possession have a somewhat loose and crumbly