March 9, 1893] 



NATURE 



437 



while there are also indications in the relative sizes of the 

 leaves of others that the climate was milder. Perhaps 

 the Alps were less elevated and the sea nearer at the time, 

 but interest is given to the problem by the undoubted 

 presence of Rhododendron ponticum, which at present 

 only flourishes in a much warmer climate far to the east, 

 but, from its discovery in other localities, was evidently 

 thoroughly indigenous in the Alps. The author regards 

 the flora as a relic of the " steppe-flora '' which then spread 

 over the greater part of Europe, and of which numerous 

 traces still exist, especially in Switzerland and Lower 

 Austria, where plants of Oriental facies, such as the yew, 

 box, holly, Ephedra, Sumach, hornbeam, feather-grass, 

 maidenhair, &c., are its lingering remains. 



The work is carefully prepared, doubtful determinations, 

 except in the case of the Arbutus and a new buckthorn 

 allied to Rhamnus latifolia of the Canaries, are eschewed, 

 and the photographic illustrations, pencilled over by the 

 artist, are extremely satisfactory. J. S. G. 



Observational Astronomy. . By Arthur Mee, F.R.A.S. 

 (Cardiff: Daniel Owen and Co., 1893.) 



This small book should serve the purpose for which it is 

 issued ; the object being to provide the beginner with an 

 inexpensive treatise to enable him to become familiar with 

 and interested in the practice of observational astronomy. 

 For this reason the author limits himself to the purely 

 descriptive side of astronomy, dealing with the sun, 

 planets, comets, and meteors, giving numerous references 

 where necessary. Short chapters are given on eclipses, 

 transits, occupations, and " the sidereal firmament," the 

 latter treating of double and coloured stars, &c. The 

 chapter on the telescope contains many practical hints, 

 besides numerous woodcuts, while that devoted to the 

 moon is very pleasant reading, and gives a good account 

 of the more general features. The illustrations, as will 

 be gathered from the above, are very numerous, many of 

 them being from the pen of the author himself. With 

 respect to these, we must add that the one given on p. 72 of 

 the Orion nebula does not remind us of the most beautiful 

 object in the heavens, while on p. 66 Donati's comet is 

 depicted minus the two long streamers which made this 

 object so striking. The book concludes with a short 

 obituary of the Rev. T. W. Webb and an appendix con- 

 taining brief contributions from Denning on comets and 

 meteors. Gore on variable and temporary stars, Seabroke 

 on double star measurement, and a few others. 



W. J. L. 



Mechanics and Hydrostatics for Beginners. By S. L. 

 Loney, M.A. (Cambridge University Press, 1893.) 



This is the latest addition to the series of elementary 

 text-books recently launched by Mr. Loney. The same 

 high standard of excellence is maintained, and the author 

 must again be congratulated on his efforts to place in the 

 hands of a beginner a book which will give him correct 

 ideas of the laws and principles which are included in a 

 study of mechanics. 



It consists of three parts, statics, dynamics, and hydro- 

 statics, each part contaming the usual chapters. If the 

 reader should fail to understand the chapter on the laws 

 of motion, he must attribute it either to his want of ability 

 or the nature of the subject, for we fail to see how the 

 author could improve his remarks on this part of the 

 subject. We are glad to observe that the words " rate of 

 change" find their way into the statement of the second 

 law, for its definiteness is increased thereby. More than 

 the usual care appears to have been devoted to the 

 selection of suitable examples ; some of them are ex- 

 ceptionally good, and thus add to the usefulness of the 

 book. Occasionally the trigonometrical ratios are used, 

 NO. I 2 19, VOL. 47] 



but their definitions will be found in the appendix ; we 

 are afraid, however, that the suggestion that their values 

 for certain angles should be committed to memory is not 

 a wise one. G. A. B. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. ^ 



The Glacier Theory of Alpine Lakes. 



The letter of the Duke of Argyll against the theory of the 



formation of alpine lakes by glacial action shows such an amount 



of misconception of the theory itself, and so completely ignores 



I the great weight of evidence in its favour, that a few words on 



I the other side seem desirable. 



The Duke says that glaciers "do not dig out," do not '"act 

 like a ploughshare," but, when moving down a slight incline do 

 " scoop," as well as rub down and abrade. No observer of 

 glaciers has ever stated, so far as I know, that they do "dig 

 out," and it is equally erroneous to say that they " scoop," for 

 that implies that it is the end of the glacier that acts. But the 

 end is its weakest point, where it is melting above and below, 

 and where consequently it can do practically nothing. The 

 whole action of a glacier is a grinding action, and its grinding 

 power is greatest where it is thickest, and where, consequently, 

 it presses on the rocks with the greatest weight. The result of 

 this grinding is seen in the muddy stream issuing from all exist- 

 ing glaciers ; while the well-known " till " is the product of the 

 rock grinding mill of ancient glaciers and ice-sheets. 



Notwithstanding the Duke's disbelief in ice-sheets I venture 

 to think that their former existence has been demonstrated both 

 in Scotland and Ireland ; but leaving this point, I wish to make 

 a few remarks on the extreme inadequacy of the earth-movement 

 theory to account for the facts. In the first place it is certain 

 that no alpine lake can possibly have a long life, geologically 

 speaking. In the course of a few thousands of years, certainly 

 in less than a hundred thousand, all alpine lakes would be filled 

 up by the sediment brought into them. It follows that all the 

 existing lakes must have been formed about the same period, and 

 that, geologically, a very recent one, and corresponding aj^proxi- 

 mately with that of the well-known glacial epoch. But if these 

 lakes were all formed by earth movemenls, either just before the 

 glacial epoch came on, or during its continuance, or afterwards 

 we have to explain the remarkable fact that such movements 

 only occurred within the limits of glaciation, never beyond 

 those limits. In Wales, Cumberland, and Scotland, in the Alps, 

 in Scandinavia, in Finland, in the northern United States and 

 Canada, in Mongolia and Thibet, in Tasmania and New 

 Zealand, we have thousands of rock-basin lakes, amid palpable 

 I signs of glaciation. But the moment we pass beyond the 

 glaciated districts, mountain lakes abruptly cease. There are 

 hardly any in Spain, none in the Great Atlas, none in Sardinia 

 or southern Italy, except in the volcanic areas and away from 

 the mountains, none in any of the West Indian islands with 

 their fine mountain-ranges, none in the peninsula of India or 

 in Brazil. And there is exactly the same distribution of fiords. 

 We have them in Norway, irj West Scotland, in Alaska, in 

 South-West America, and in New Zealand, all characterised 

 by deeper water within than at their outlets, and all in glaciated 

 countries, but nowhere else in the world. 



Now it is simply impossible to believe that at a very recent 

 period there should have been earth -movements of such a char- 

 acter as to produce lakes, but always in glaciated districts and 

 never beyond them, unless the movements were a result of the 

 glaciation. This has not, I believe, been yet suggested ; but, 

 in view of the modern theory that any considerable loading of 

 the surface produces subsidence, it is at least a possible explana- 

 tion. But there are some important facts that seem more in 

 favour of the grinding out of the lake-basins by the enormous 

 weight of ice accumulated over their sites during the height of 

 the ice-age. Looking at a geological map of the Alps it will be 

 seen that most of the lakes are more or less bordered by tertiary 

 or secondary rocks. Lakes Annecy and Bourget are in miocen<? 



