CHAP. XT.

BY THE EHOSIVE ACTION OF G1ACIEES.

359

as the Alps that unequal movements in very limited areasare most strikingly exemplified. The huge contortions andvertical position of the older rocks sufficiently show how invery small areas the greatest inequalities of movement havetaken place, and it is perfectly unwarrantable to supposethat those movements which carried up miocene strata to aheight of 9,000 feet and gave them a dip of many degrees,were entirely suspended during the immense lapse of timeduring which the glaciers of the Alps swept through thevalleys of Switzerland and Piedmont. In the countlesspost-miocene ages which preceded the glacial period therewas ample time for the slow erosion by water of all theprincipal hydrographical basins of the Alps , and the sites ofall the great lakes coincide, as Professor Eamsay truly says,with these great lines of drainage. The lake-cavities do notlie in synclinal troughs, following the strike and foldingsof the strata, but often, as the same geologist remarks,cross them at high angles ; nor are they due to rents orfissures, although these, with other accidents connected withthe disturbing movements of the Alps , may sometimes havedetermined originally the direction of the valleys. Theconformity of the lake-basins to the principal watercoursesis explicable if we assume them to have resulted from in-equalities in the upward and downward movements of thewhole country in pleistocene times, after the valleys wereeroded.

We know that in Sweden the rate of the rise of the landis far from uniform, being only a few inches in a centurynear Stockholm , while north of it, and beyond Gefle, itamounts to as many feet in the same number of years. Letus suppose, with Charpentier, that the Alps gained in heightseveral thousand feet at the time when the intense cold ofthe glacial period was coming on. This gradual rise wouldbe an era of aqueous erosion, and of the deepening, widening,