In the lecture on the Savoy Alps in 1863 he had referred to a hint of Saussure's that the contorted beds of the limestones might possibly be due to some sort of internal action, resembling on a large scale that separation into concentric or curved bands which is seen in calcareous deposits. The contortions of gneiss were similarly analogous, it was suggested, to those of the various forms of silica. Ruskin did not adopt the theory, but put it by for examination in contrast with the usual explanation of these phenomena, as the simple mechanical thrust of the contracting surface of the earth. In 1863 and 1866 he had been among the Nagelflüh of Northern Switzerland, studying the puddingstones and breccias. He saw that the difference between these formations, in their structural aspect, and the hand-specimens in his collection of pisolitic and brecciated minerals was chiefly a matter of size; and that the resemblances in form were very close. And so he concluded that if the structure of the minerals could be fully understood a clue might be found to the very puzzling question of the origin of mountain structure. Hence his attempt to analyze the structure of agates and similar banded and brecciated minerals, in the series of papers in the _Geological Magazine_;[15] an attempt which though it was never properly completed, and fails to come to any general conclusion, is extremely interesting as an account of beautiful and curious natural forms till then little noticed by mineralogists. [Footnote 15: August and November, 1867, January, April and May, 1868, December, 1869, and January, 1870, illustrated with very fine mezzotint plates and woodcuts.] A characteristic anecdote of this period is preserved in "Arrows of the Chace."