178 GLACIAL HISTORY. 



beds are met with of which the materials have come from the 

 Valais. The same phenomenon is presented by the southern 

 slope of the Alps, where great beds of sand and gravel extend 

 down into the plain of Italy,, as, for instance, to the south of the 

 Lago Maggiore. 



These stratified pebble-beds are so like the gravels deposited 

 by the Swiss mountain-streams, that, without doubt, they were 

 produced in the same manner. 



We must, however, distinguish from them the unstratified 

 gravels which have been characterized as the Erratic formation, 

 and which consist of unstratified masses of sand and stones, and 

 of isolated blocks of all sizes. Where they lie together in great 

 masses, large and small fragments of rock are heaped together 

 without any order : some of them are rounded ; others still pos- 

 sess sharp edges and angles ; and their surfaces are not unfre- 

 quently traversed by straight striae or scratches, sometimes 

 parallel to each other, sometimes crossing in various direc- 

 tions. The stratified drift is uniformly spread over the bot- 

 toms of the valleys, and is only cut through by brooks and 

 rivers, which wear it away and form steep cliffs, whilst the un- 

 stratified drift forms chains of hills standing out more or less 

 abruptly from the surrounding surface. These chains frequently 

 follow the slopes of valleys and run parallel with them, or they 

 cross the valleys in the form of crescent-like ramparts or 

 moraines. 



The most remarkable of these moraines, for the investigation 

 of which we are chiefly indebted to M. A. Escher de la Linth, 

 are shown on the geological map at the end of this volume. 

 Two such moraines occur in the neighbourhood of Berne one 

 near Muri, a Swiss mile, south of the town, the other in the city 

 itself. Several moraines in the Cantons of Lucerne and Argovia 

 are still more distinctly marked : thus a curved chain of hills 

 from 100 to 200 feet high, and of about the same breadth, sur- 

 rounds the northern end of the Lake of Sempach, resting at one 

 end against the boulder-deposits of the hill of Sempach, and 

 at the other extremity abutting on the masses of rocks of 

 Wartensee. A second mound, cut through by the Sur, traverses 

 the same valley lower down near Staffelbach, and runs towards 

 Mooslerau. The northern extremity of the Lake of Baldegg is 



