Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/191

 beds in the immediate neighbourhood, through being let down by faults, is a phenomenon familiar to every geologist, and, indeed, is illustrated by wonderful examples cited in the present memoir. That landslips acting during the Glacial epoch might have produced a similar result on a small scale is clear ; and, indeed, examples of the kind have presented themselves to me during my survey of districts thickly covered with drift in the Midland counties of England*. I have already shown reasons for believing that the Secondary strata were largely developed in the Elgin district.

On the other hand, the principal objection which has been raised to the hypothesis that the Linksfield mass is a boulder†, namely that of its great size, has been effectually disposed of by the discovery of undoubted transported masses of equal, and even greater dimensions, imbedded in the Boulder-clay of other districts‡.

It is not my purpose to attempt to decide between these two hypotheses, both of which appear to harmonize equally well with all the phenomena of the case — the glacially striated and polished rock at the bottom of the section, the overlying and underlying Boulder-clay, containing detached fragments of the same beds, and sometimes filling fissures in the principal mass, and the contorted, cracked, and sometimes dislocated appearances presented by the latter. The two hypotheses have some points in common ; for it is evident that in order to account for the transportation of such enormous masses by means of ice rafts, we must suppose that they have been deposited on the surface of the ice-foot by means of landslips. Perhaps it will be more logical in all such cases to avoid calling in the agency of these vast ice-floats except in the cases (of which there are many) in which it can be clearly shown not only that the rocks composing the masses are absent in the neighbourhood now, but that it is impossible that they could have existed in the vicinity as escarpments during the Glacial period.

The section at Linksfield is now unfortunately closed, the quarrying of the limestone below the shales and Boulder-clay having been abandoned. Admirably detailed descriptions of the succession of the beds, however, have been published by Malcolmson§, Duff||, Brickenden¶, and Moore**.

Although the Linksfield beds are highly fossiliferous, there is considerable difficulty in fixing their exact age. The fallacy of the arguments derived from the mineral characters and the succession of the beds, on the strength of which they have been successively

be described in a forthcoming memoir of the Geological Survey.
 * These and many examples of transported masses of enormous dimensions will

† Symonds, Edin. New Phil. Journ. New Ser. vol. xii (1860) p. 100.

‡ See Morris, Quart. Journ. Geol. Soc. vol. ix. (1853) p. 317; Ramsay, ibid, xxvii. (1871) p. 252 ; also Fisher, Geological Magazine, vol. v. (1868) p. 407 ; and Bonney, ibid. vol. ix. (1872) p. 403.

§ Proc. Geol. Soc. vol. ii. p. 667 ; and Edin. New Phil. Journ. New Ser. vol. ix. (1859) p. 48.


 * Sketch of the Geology of Moray, p. 15, plate iii.

¶ Quart. Journ. Geol. Soc. vol. vii. (1851) p. 291.


 * Ibid. vol. xvi. (1860) p. 440.

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