NATURE 



477 



THURSDAV, SEPTEMBER 15, 1904. 



.V£ir .4.VD OLD \1E\XS OX GLACIATION. 



Die Gletscher. By Dr. Hans Hess, konigl. gymnasial- 

 Professor in Ansbach. Pp. xii + 426. (Brunswick: 

 F. Vieweg und Sohn, 1904.) Price 15 marks. 



THE author of this closely written treatise reminds 

 us that it is nineteen years since Heim issued 

 liis classical " Handbuch der Gletscherkunde," and 

 that the numerous additions to our knowledge since 

 1885 may w'ell be brought together in a convenient 

 form. Dr. Hess has an intimate personal knowledge 

 of European glaciers, on which he has made patient 

 and numerical observations ; and in the difficult matter 

 of the theory of glacier-motion he has had the cooper- 

 ation of Prof. Finsterwalder, of Munich. The work 

 of Finsterwalder, indeed, is in many ways an in- 

 spiration throughout the book, but the references to 

 Chamberlin, Bruckner, Drygalski. Penck, Reid, and 

 nianv others show what an immense amount of 

 material has been added to our knowledge in very recent 

 years. 



In summarising the conclusions of these authors, the 

 work of Dr. Hess becomes somewhat encyclopaedic, 

 and it will be felt, according to the idiosyncrasies of 

 the reader, that certain subjects are unduly dwelt on, 

 while others are summarily compressed. Those who 

 live in countries that were at one time buried under 

 confluent sheets of ice will wish to see an extended 

 history of Polar and Alaskan glaciers, and a further 

 discussion of the widely spread moraine-material which 

 appeared on their melting and retreat. The mention 

 (p. 388) of Karnes and Eskers as " durch die Schmelz- 

 wasser geformte Hiigel in den Schotterbanken " will 

 hardly satisfy dwellers in Britain or Scandinavia, not 

 to say the Prussian plain ; nor does it represent the 

 views recentlv accepted by Prof. Jas. Geikie, from 

 whose work it is professedly a translation. We ought, 

 however, to be willing to refer to memoirs on special 

 districts when pursuing inquiries such as these, and 

 we may w-ell be grateful to Dr. Hess for the new details 

 brought to our notice from the regions in which he 

 himself has studied. 



The book opens with a review of previous observ- 

 ation, in which priority is accorded to John Playfair 

 for realising the meaning of erratic blocks so far back 

 as 1802. The physical characters of ice are then dis- 

 cussed, and full stress is laid on the recognition of 

 ice as a viscous body, yielding to pressures and adapt- 

 ing itself to its surroundings. Glacier-ice (p. 20) 

 >uffers some reduction 'in plasticity owing to the 

 admixture of sand ,and dust. The discovery by 

 McConnel and Kidd, and by Emden, of the plasticity 

 of the individual ice-crystal led Emden (p. 316) to re- 

 mark that a glacier consisting of a single crystal at 

 the temperature of its melting point would move 

 precisely as a granular glacier. Regelation, as an 

 explanation of glacier-motion, though still holding its 

 own in physical text-books, has been set by geologists 

 in the second place in recent vears. In the regener- 

 ition of fractured glaciers, however, as Hess points 

 mil, this phenomenon plavs a mr>-i Imn.irt.mt i^.irt. 

 XO. 1820, VOL. 70] 



\\"e could wish that the tenth section, on the theory 

 of glacier-movement, had followed closely on the first, 

 and had thus offered an explanation of much that is 

 obscure in the earlier chapters of the book. The 

 development of Finsterwalder's " Stromlinien " is 

 greatly needed during the discussion of moraines, and 

 readers of so special a treatise are naturally familiar 

 enough with general physical geography and the form 

 of glaciers to understand the exposition of Finster- 

 walder's views at an early stage. This exposition, 

 from p. 325 onward, shows how every point in the 

 surface of the firn-basin is connected by a " Strom- 

 linie " with a corresponding point on the surface of 

 the glacier lower down. The ice-particle enters the 

 firn at one end of the line, by deposition from the atmo- 

 sphere, and disappears from the glacier, by melting or 

 evaporation, at the other end of the line. In between, 

 it has had a course within the ice-mass, longer or 

 shorter, according to the form of the rock-floor and of 

 the bounding walls. The lower boundary of the firn 

 marks the line of division between the area where the 

 flow-lines enter the glacier and that in which they 

 emerge upon its surface. While a " Stromlinie " never 

 lies entirely on the glacier-surface, a " Bewegungs- 

 linie " is (pp. 138 and 327) the course of a stone 

 dropped upon and remaining on the surface. Shortly, 

 "Stromlinien" emerge at all points along " Bewe- 

 gungslinien," but do not coincide with them. 



Dr. Hess regards the stratified structure of glacier- 

 ice as essentially arising, by natural conditions and 

 irregularities of deposition, in the area of the firn; the 

 appearance becomes intensified by streaming out and 

 extension lower down (p. 173), but has nothing to do 

 with internal pressures. Experimental evidence of, 

 this conclusion is provided. .An interesting case of 

 unconformity in the bedding of ice-layers is quoted 

 and illustrated from Finsterwalder on p. 177. 



The title of the seventh section, " Eis und Fels," 

 reminds us that massive ice is as much one of the 

 rocks of the earth's crust as desert-sand or a reef of 

 coral. Marine limestones are, for instance, formed of 

 material withdrawn from invisible solution in the sea;, 

 on one side they may receive almost molecular addi- 

 tions, on the other side they may disappear again by 

 solution. An ice-mass is similarly added to or removed 

 at different points, but it is none the less a rock. Its 

 plastic behaviour, however, among other rocks has led 

 us to think of it as a thing apart, just as we sometimes 

 forget that mercury has a crystallographic form. The 

 chapter in question will attract attention on account 

 of its treatment of moraines, and the belief of the 

 author in the rapidity of the erosion that takes place 

 upon the glacier-floor. From personal observations, 

 which are now being carried further, he estimates this 

 erosion, in specially active cases, as indicating a re- 

 duction of the floor-level by 3 cm. per annum. Allow- 

 ing for the additional influence of water-erosion, which 

 he considers to be far less than that of the moraine- 

 laden ice, he uses the figure of 3 cm., somewhat 

 adventurouslv, in calculating (p. 376) the age of some 

 of the larger valleys of the Alps. 



A fine picture (p. 35) is given to show how the fissile 

 structure of rocks affects their mode of weathering by 

 ihi- ire. The author holds ih:ir lar<re blocks are re- 



