MORAINES—GLACIER TABLES.

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between the wall and the ice, producing friction, and an inclined shore,b, on which the lateral moraine has been deposited. There is alsoshown, at c, the position of an ancient moraine, deposited at a timewhen the glacier was elevated enough to have submerged the pro-montory a; one of the medial moraines is shown at d: The ice rises toa greater height under it than at any other part, owing to a circum-stance to be mentioned immediately. An exact idea of the generalphenomena of moraines will be obtained from the large map of theMer de glace of Chamouni accompanying this work, and from PlateII., which gives a view of it.

The presence of these blocks upon the surface of the glacier, and ofthe fine sand and debris which is produced by their trituration, givesrise to a peculiar and striking class of phenomena, easily explained, yetat first sight most astonishing. The surface of a glacier is usuallydivided by numerous rents or crevasses, stretching as we have seen,often nearly from side to side, and into these rents blocks are con-tinually falling. Still, the fact is, that the moraines remain upon thesurface, and unless after a very long or very uneven course, they arenot dissipated or ingulfed. On the contrary, the largest stones areset on a conspicuous pre-eminence,—the heaviest moraine, far fromindenting the surface of the ice, or sinking amongst its substance, ridesupon an icy ridge as an excrescence, which gives to it the character ofa colossal back-bone of the glacier, or sometimes appears like a noblecauseway, fit indeed for giants, stretching away for leagues over mo-notonous ice, with a breadth of some hundreds of feet, and raisedfrom fifty to eighty feet above the general level. Almost every stone,however, rests on ice; the mound is not a mound of debris, as itmight at first sight appear to be. Nor is this all. Some block ofgreater size than its neighbours, covering a considerable surface of theice, becomes detached from them, and seems shot up upon an icypedestal, in the way represented in the Frontispiece, from a real andvery striking example which occurred in 1842 on the Mer de glace ofChamouni. This apparent tendency of the ice to rise wherever it iscovered by a stone of any size, results from the fact, that its surfaceis depressed every where else by the melting action of the sun and