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that takes its beginning on the northern face of the Dauphin^ Alps . The crystalline rocks appear again in the watershed ofthe Pennine chain, and extend almost without interruption overit and the Graians. For several miles they are not found uponthe right bank of the Rhone, hut when, between Leuk and Yisp,the course of the river is deflected from its usual south-westerlydirection, they cross the valley and form the greater part of thehigher Oberland . Thence, with occasional slight breaks, theyoccupy the whole Alpine district between the Italian Lakes,the Valtelline, and the Upper Rhine , and are extensively de-veloped in the tangled knot of mountains in which rise thestreams supplying the Hinter Rhein and the Inn. In theTyrol they form the watershed between Germany and Italy ;the great central ridge, between the valley of the Inn on oneside and the valleys of the Rienz and Drave (the long trenchof the Puster-thal) on the other, being wholly composed ofthem.
The compact colierents vary considerably in their power ofresisting the action of weather; but as a rule, sandstones aremuch more easily disintegrated than limestones. The formerhowever, though largely developed in the subalpine regionof Savoy and Switzerland , about the lakes of Annecy , Geneva ,Neuchatel , Zurich , and Constance, are very rare among thehigher Alps , and have then been so much altered by the actionof heat that they may rather be classed among the crystallinerocks, their grains being often fused together so as to form acompact mass. The limestones as a rule are tolerably hard,and in many cases have so far been altered by heat as to bemore or less crystalline. They, interbedded with the slatycoherents, abound over a large portion of the Alps . In thewestern district they are almost wholly absent upon the easternslopes of the watershed, but are developed extensively aroundthe crystalline zone which extends, nearly without intermission,from the Pelvoux group to Mont Blanc ; the Alps of southern