Notices of Memoirs — Prof. Heim on Formation of Mountains. 133 



shows that the G-larus double fold is the mechanical continuation of 

 the central mass of the Finsteraarhorn — that the latter is also formed 

 by lateral displacement — that these different mountains are of the 

 same age, and must have been produced during the Miocene or 

 Pliocene epoch. 



The last part of the first volume treats of the form of the surface ; 

 and in different chapters are considered successively — glaciers, the 

 effects of Quaternary glaciers in the district, avalanches, springs, and 

 specially the relations of erosion to the present configuration of the 

 surface. Denudation has destroyed absolutely the original shapes 

 which would correspond to the internal structure of the mountains. 

 The Alps in our day have no longer half their pristine mass, more 

 than half has been removed by erosion. We recognize in the form 

 of terraces, on the sides and floors of valleys, the remains of old 

 beds up to a height of 6,500 feet above the level of the present 

 bed. These terraces are entirely independent of the structure of 

 the mountain, but they correspond with those of the confluents of 

 the same river, and differ in the valleys formed by the different 

 main rivers. 



Professor Heim thinks that the necessary conclusion from these 

 facts, is that the valleys of the Alps are due entirely to erosion. If 

 fissures or synclinal lines have in the first place fixed the direction, 

 this must have been far above the present peaks and actual crests 

 and in rock which has long disappeared. Many of the large rivers 

 existed before the mountains which now surround them. Erosion 

 acts from the mouth of a valley upwards, the valleys eat more and 

 more back into the hills, and are often intersected. In a special 

 resume the author enumerates the arguments with which he meets 

 those geologists who assume that mountain- valleys are ruptures of 

 the earth's crust. 



In the second volume the first part is entitled " Mechanical dis- 

 tortion of rocks by the elevation of mountains." The phenomena of 

 folding, rupture, cleavage, etc., are examined as to their physical 

 relations. The outcome is, that distortion without fracture can be 

 produced in rocks which had already acquired their present hardness. 

 The new observations belonging to these phenomena are grouped 

 under sixteen laws. The author developes the result of an examina- 

 tion by the microscope of rocks crushed by pressure — this can even 

 produce chemical changes. The following chapter contains the 

 physical explanation of these phenomena — it may be stated shortly 

 thus : At a certain distance below the surface rocks are found under 

 a pressure much greater than their power of resistance ; this pressure 

 spreads in all directions as in a liquid. Eocks are thus reduced to a 

 latent plastic state. Directly that a new force like lateral pressure — 

 such as causes the elevation of mountains — acts on the mass, a 

 homogeneous change of form results. Neighbouring surface rocks 

 are distorted in yielding. The thrusts which have acted during 

 crumpling of the Alps are in accordance with theory and experience. 



A second part of the volume is devoted to the central masses of the 

 Alps. Some geologists imagine that these crystalline centres play 



