THE ICE AGE AND ITS WORK. 785 



&n unstratified mass of clay or mud, through which a variety of angular and 

 rubbed stones were scattered, and a marked proportion of the whole were pol- 

 ished and scratched, and the clay rendered so compact, as if by the incumbent 

 pressure of a great mass of ice, that it has been found necessary to blow it up 

 with gunpowder in making railway cuttings through part of it. A marble rock, 

 of the age of our Portland stone, on which this old moraine rests has its surface 

 polished like a looking-glass, displaying beautiful sections of fossil shells, while 

 occasionally, besides finer striae, there are deeper rectilinear grooves, agreeing in 

 direction with the course in which the extinct glacier moved according to the 

 theory of M. Guyot before explained.* 



It is evident that, to have produced such effects as are here de- 

 scribed, the glacier must have extended much beyond Soleure, 

 .and have been very thick even there. It thus proves to demon- 

 stration that a glacier can travel for a hundred miles over a gen- 

 erally level country, that it can pass over hills and valleys, and 

 that, even near its termination, it can groove, and grind, and pol- 

 ish rocks, and deposit large masses of hard bowlder clay. And 

 .all this was done by a single glacier issuing from a comparatively 

 narrow valley, and then spreading out over an area many times 

 greater than that of its whole previous course. In this case it is 

 clear that such a vast mass of ice, constituting a veritable ice- 

 sheet on a small scale, could not have derived its motion solely 

 from the push given to it by the parent glacier at St. Maurice. 

 Neither could gravitation derived from the slope of the ground 

 have affected it, for it passed mostly over level ground or up 

 .slopes, and its termination at Soleure is actually nearly two hun- 

 dred feet higher than its starting point at the mouth of the val- 

 ley below St. Moritz ! There remains as a cause of motion only 

 the slope of the upper surface of the glacier, the ice slowly flow- 

 ing downward, and, by means of its tenacity and its viscosity on 

 .a large scale, dragging its lower portion still more slowly over 

 the uneven or upward sloping surface. This mode of motion will 

 be discussed later when dealing with the origin of lake-basins. 



No doubt at this epoch of maximum glaciation the ice-sheet 

 extended over the whole country between the Bernese Alps and 

 the Jura, and the downward flow of the lateral glaciers along the 

 valley of the Sarine, Aare, and other rivers flowing toward So- 

 leure greatly assisted the general onward motion. But the fact 

 remains, and it can not be too strongly insisted on, that here we 

 have a veritable ice-sheet moving over hill and valley, carrying 

 on its surface quantities of erratic blocks, rounding, striating, and 

 polishing the rocks over which it passed, and with the material 

 thus crushed and ground away forming great deposits of bowlder 

 clay, much of which still remains, although enormous quantities 



* The Antiquity of Man, fourth edition, p. 349. 

 VOL. XLIV. 58 



