The formation of a new road on the banks of this lake, has exhibited some instances of the contortions of mica slate, which are deserving of notice. I have attempted to give a notion of them in the accompanying sketches (Pl. 31. fig. 1, 2.—Pl. 31*, fig. 3 only.—Pl. 32, fig. 1.[errata 1]) as it is not possible to procure specimens of the magnitude requisite for that purpose.
It would be superfluous to add any thing to the observations on the inflexion of strata, in the "Illustrations of the Huttonian theory," where this subject is ably treated. But as they consist chiefly of remarks on the continuous inflexions of extensive strata, it will not be useless to notice the more complicated curvatures which take place in the smaller masses. In a brief notice on certain waving lines of colour occurring in killas at Plymouth Dock, transmitted last year to the Society, I suggested the difficulties which attended a solution of this question, the disposition of the colour having no relation to the laminæ of the schist. But in the contortions of the mica slate, the laminæ themselves are waved, and we have only therefore to enquire into the conditions requisite to the production of this appearance.
It is evident on inspection of the sketches, and will be equally so to those who shall inspect the rocks themselves, that, if the several laminæ which compose any given mass, were to be now rendered flexible, they could not be reduced to continuous straight lines, without materially changing the relations of their several lengths, and thus altering the figures of the rocks which now contain them. It is therefore evident, that no general force acting on a large mass has been the cause of these curvatures, but that they have been produced by the application of numerous partial forces acting on different parts, and capable of stretching those sets of laminæ on which the
- Original: fig. 3. was amended to fig. 3 only.—Pl. 32, fig. 1.: detail