Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/190

 the beds at Linksfield to those of the Rhaetic formation in the southwest of England, and he showed that there exists some palaeontological evidence in favour of identifying the two series. In this view he was confirmed by Professor Rupert Jones*.

The remarkable position of the mass of Secondary strata at Linksfield has given rise to a number of hypotheses to account for it. The chief of these are as follows : —

(1) That the stratified clays and limestones once rested immediately upon the Triassic limestone, and that the foot of a glacier or iceberg forced the two sets of strata asunder, carrying with it a mass of glacial detritus and scoring and polishing the hard surface of the lower rock. This hypothesis appears to have been first suggested by Mr. A. Robertson, of Inverugie, and Captain Brickenden†, and to have received the sanction of Professor Agassiz.

(2) The hypothesis suggested by Sir Charles Lyell at the Aberdeen Meeting of the British Association (1859) is as follows : — " That a range of cliffs, of Triassic and Lower Liassic beds, rose above the Vale of Elgin during the glacial epoch, when ice rafts and drifting bergs, with all the phenomena of an Arctic sea, swept down that vale, then a frith, and that the siliceous cornstone was then the actual sea-bed. The icebergs and drifting masses undermined the soft marls of the Upper Trias and Lias, and in time produced a landslip. The whole side of a sea-cliff slipped down from its position, on to a beach of Boulder-clay, without any bouleversement of the strata "‡.

(3) The view first put forward by Dr. Gordon § and other local observers, and since advocated by Professors Geikie and Ramsay||, is, that the mass of Linksfield and similar masses in the neighbourhood are really great transported blocks, which have been carried by ice across the sea in which the Boulder-clay was formed, and quietly deposited at the bottom by the stranding and gradual melting of the ice rafts.

The results of the more careful and exact studies of the modes of ice-action made during recent years have been such as, I believe, to lend but little support to the first of these hypotheses, while on the contrary they have, by furnishing undoubted examples of analogous action and by showing the futility of supposed objections, removed many of the difficulties which prevented the acceptance of either of the two other hypotheses.

The preservation of a mass of strata, higher in the series than the


 * Monograph of the Fossil Estheriae (Palaeontographical Society, 1862), pp. 74-77.

† Quart. Journ. Geol. Soc. vol. vii. (1851) p. 291 See also A. Robertson, in Anderson's ' Guide to the Highlands,' 3rd ed. (1851) p. 344 : a similar view appears to have been hinted at by Mr. Duff, ' Sketch of the Geology of Moray ' (1842).

‡ Symonds in Edin. New Phil. Journ. New Ser. vol. xii. (1860) p. 100, and Quart. Journ. Geol. Soc. vol. xvi. (1860) p. 459.

§ Edin. New Phil. Journ. New Ser. vol. is. (1859) p. 52. Ibid. vol. iv. (1856) p. 223.


 * Quart. Journ. Geol. Soc. vol. xxvii. (1871) p. 252.