On the side of the same lake, is another instance of bent strata, in a mountain, of which the beds are horizontal in the lower part, but are bent at one end upwards, in the form of the letter C. The horizontal part is of great extent, and the rock is also calcareous,[101]
[101] Ibid. § 337.
The Montagne de la Tuile, near Montmelian, receives its name from the beds of rock being incurvated in form of a tyle.[102] Among secondary mountains, the same kind of phenomena are observed, though less frequently, and with less variety of inflection. The chain of Jura is secondary, and the beds which compose it are of limestone, or of grit: they are bent in such a manner, that in a transverse section of the mountain, each layer would have the figure of a parabola.[103]
[102] Ibid. vol. iii. § 1182, and plate i.
[103] Ibid. tom. i. § 334.
201. The Pyrenees furnish abundance of phenomena of the same kind, as we learn from the Essai sur la Mineralogie des Pyrenées. The calcareous strata of the valley of Aspe, represented plate v. of that work, deserve particularly to be remarked.
202. Our own island abounds with examples of the bending and inflection of the strata, especially the primary, and many of them very much resembling those in the Alps and Pyrenees. On the top of the mountain of Ben-Lawers, in Perthshire, there is a rock, the face of which exhibits a section of a great number of thin equidistant layers, bent backwards and forwards like those described by Saussure; and this unequivocal proof of the rock having once existed in the state of a flexible and tenacious paste, is rendered more striking, by the great elevation of the spot, and the ruggedness and induration, both of the stone itself, and of every thing that surrounds it. Many other mountains in this tract consist of a schistus, which is talcose rather than micaceous, and subject, in a remarkable degree, to the sort of sinuosity and inflection here treated of.
The appearances of the primary strata on the coast of Berwickshire, have been already mentioned, as affording much valuable instruction in geology. They also exemplify the waving and inflection of the strata on a large scale, and with great variety. A section of some of them is given by Dr Hutton, in his Theory of the Earth, vol. i. from a drawing made by Sir James Hall. The nature of the curve superficies into which the schistus is bent, is the better understood from this, that, besides transverse sections from north to south, the deep indentures which the sea has made, and the projecting points of rock, exhibit many longitudinal sections, in a direction from east to west.
203. The dock-yards at Plymouth are in several places cut out of a solid rock of primary schistus, singularly incurvated. The inflections are seen there to great advantage, being exhibited in three sections, at right angles to one another, transverse, longitudinal and horizontal.
204. From these instances, to which it were easy to add many more, two conclusions may be drawn. The first of these is very obvious, viz. that the strata must have been pliant and soft when they acquired their present form. The bending of an indurated bed of stone into an arch of great curvature, and without fracture, as in the preceding examples, is a physical impossibility. Saussure has indeed observed a fracture to accompany the bending, in one or two cases; but it is an uncommon phenomenon, and, where it happens, must no doubt be understood to indicate an imperfect flexibility. Now, if it be granted that the strata were at any time soft and flexible, since their complete formation, it will be found impossible to deny their having been softened by the application of heat.