CHAPTER I LAKE BASINS AND THEIR RELATION TO GLACIERS-THE PARALLEL ROADS of glenROY— ESKERS, ETC. for it is generally began, the whole The other chapter IN the preceding chapters we have endeavoured to collect the principal facts relating to ice and its work. The one gives a sketch of the scenery, and describes the deposits in a land which was formerly overspread with ice. For this Switzerland was selected rather than Scandinavia, because its situation permits us to attribute all its deposits, dating from the Glacial Epoch, to the action of land-ice; admitted that, since this epoch country has been above the sea. attempts to depict regions where a Glacial Epoch now prevails, in which also the work of ice, both on land and by sea, can be studied. Greenland, for this purpose, is exceptionally instructive, because it must reproduce very closely the conditions prevalent in the north-western part of the European continent during the Glacial Epoch, and thus must throw light on certain difficult problems which the latter presents. These we pass on to consider. The first-the vexed 79 question of the part played by large masses of ice in the excavation of lake basins-has a less direct connection with Greenland, and will be discussed in the present chapter, together with other collateral subjects. The second practically amounts to this— How far can the work and deposits of land-ice be distinguished from those which are more immediately due to floating ice? This question can be most conveniently discussed in connection with the history of the British Isles during the Glacial Epoch, and is thus reserved for the next chapter. Each question at the present time is a battle-field in geology, and though it will be convenient to consider the two apart, the one cannot be wholly separated from the other. In either case we shall do our best to state the facts which have been ascertained, to give the rival interpretations, and to indicate the points in each which appear to be strong or weak, when they are regarded in the light of results established by the study of cases where either there can be no controversy or the differences of opinion, comparatively speaking, are but slight. In the year 1862 the late Sir A. Ramsay1 sought to prove that the lakes in and about the chain of the Alps had been excavated by the ancient glaciers. The following is a brief summary of his paper, which, whether the conclusions of the distinguished author be ultimately accepted or not, did great service 1 Quart. Jour. Geol. Soc. xviii. (1862), p. 185. in clearing away misconceptions by which the inquiry previously had been much obscured :— (1.) None of these lakes lie in simple synclinal troughs, that is to say, in synclines the axis of which has a general correspondence with the longer diameter of the lake basin. As the author says: "The lake hollows in the Alps are encircled by rocks, the strikes, dips, and contortions of which often exhibit denudation on an immense scale; and in no case is it possible to affirm, here we have a synclinal hollow of which the original uppermost beds remain." Neither do they lie in any area of special subsidence, such as might be produced by the dissolving and removal of underlying masses of rock. Though this occasionally might be a cause, the number of adjacent dimples in the earth's crust, which this hypothesis not seldom would demand, and the fact that the basins often lie among rocks which are practically insoluble, is fatal to it as one of general application. (2.) The Alpine lakes cannot be hollows eroded by the rivers which still pass through them. "Running water may scoop out a sloping valley or gorge, but (excepting little swallow-holes) it cannot form and deepen profound hollows, so as to leave a rocky barrier all round." (3.) The Alpine lakes do not lie in lines of gaping fracture. This idea, which found much favour with some of the older geologists, is disposed of conclusively by showing that even the deepest and narrowest of F |