230 



NATURE 



\7uly 13, 1876 



seen of him alive by his party ; his murder at Manwyne 

 was evidently part of a scheme to attack and murder the 

 whole party, who of course returned frustrated in their 

 object. 



It is not for us to enter into any discussion as to who 

 are the real authors of the treacherous affair ; so far as 

 data permit, Sir Rutherford Alcock discusses the whole 

 question, as well as shows the value of Margary 

 and of his journey, in an Appendix. Whoever was to 

 blame, Margary himself was blameless : it is difficult to 

 regard his death as anything but an unrelieved loss : we 

 trust her Majesty's Consular Service contains many like 

 him. 



OUR BOOK SHELF 



Through Bosnia and the Herzegovina on Foot during 

 the Insurrection, August and September, 1875. By 

 Arthur J. Evans, B.A., F.S.A. With a Map and 58 

 Illustrations. (London : Longmans and Co., 1876.) 

 This is an opportune publication, and we recommend it 

 to our readers as one that will give them a good and 

 lively idea of the countries referred to and their various 

 peoples — of much interest at present in connection with 

 the Servian rising. Mr. Evans entered Bosnia at Brod on 

 the Save, went leisurely south, with various divergences, 

 through the country, reaching the sea near the mouth 

 of the Narenta and coasting along to Ragusa. Mr. Evans 

 mixed freely with all classes of the people wherever he went, 

 is well acquainted with Bosnian, and indeed with general 

 European history, is a discriminating ethnologist, and has 

 a good knowledge of botany. He studied the features 

 and habits of the people closely as he sojourned among 

 them, and gives many notes that might be found of value 

 to those who take interest both in Aryan and Turanian 

 ethnology. The people are evidently capable of good 

 things if they bad the chance and were free from oppres- 

 sion ; but Mr. Evans's observation confirms all that has 

 been said as to the impossibility of the Turk ever treat- 

 ing a Christian subject with justice or even humanity, 

 unless compelled. The book contains a map and many 

 attractive illustrations, is interestingly written, and will 

 give English readers a fair idea of a country that is 

 almost as little known to the generality as the heart of 

 Africa. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. \ 



Firths, Dales, and Lakes, Valleys and Cafions 



In Nature, vol. xiii. p. 481, you honoured me by printing a 

 notice of some writings on glacial subjects, and since then 

 many pamphlets have been sent to me. I would gladly show 

 that I have studied them. Though I do not believe in a 

 " glacial period," I have convinced myself that local glacial 

 climates, like the existing climate of Greenland and the " Arctic 

 current " have prevailed in different regions at different times, 

 and that marks of these " local glacial periods " include 

 " valleys " of certain forms, with " firths " and " lake 

 basins." Glaciation occupied the attention of the Geological 

 Society at their last meeting, when Prof. Ramsay read an 

 abstract of a paper, in which a foreign writer compared Green- 

 land and Norway. So far as I understand that writer's views 

 as to glacial action in general, I agree with him. Many 

 writers hold opposite opinions as to " the usual evidence of power- 

 ful ice erosion," and "the alleged power of a glacier to excavate 

 a depression in the earth's surface" (Judd), as to "abrasion," 

 and "the inability of glaciers to excavate except under peculiarly 

 favourable circumstances " (Bonney). Truth is learned by ob- 

 servation and by perseverance. A drop hollows a stone, not 



by force, but by frequent falling, and that truth has become pro- 

 verbial. A stream of water by flowing-, and by rolling stones, 

 makes a watercourse, and that truth is proved by every shower 

 and in every gutter. By perseverance flowing water makes a 

 deep watercourse. According to the latest official report of Dr. 

 Hayden (June 4, 1876), streams which began to flow about the 

 sources of the Mississippi, when the Rocky Mountains were 

 raised, have gone on flowing ever since in the same channels, 

 and some have worn caiions "from half a mile to a mile 

 deep," not by force, but by frequent flowing. A glacier 

 also flows. It is acknowledged that it wears and grooves 

 rock, but still it is denied that a wide deep stream of flow- 

 ing ice can make a wide deep furrow. It is said that ice 

 " abrades," but does not "erode," that it cannot "excavate," 

 unless under favourable circumstances. It is maintained that 

 flowing ice cannot hollow out a basin, though flowing water 

 does it on a small scale A^herever it flows. Much is done 

 by perseverance. As a drop hollows a stone, and water 

 a watercourse, so ice makes an ice-channel slowly ; and 

 much repetition by glacialists may in time convince sceptics 

 of that truth. Icebergs are the ends of glaciers pushed out 

 into the sea, and there launched. Some of them are 3,000 feet 

 thick. They prove their size by grounding in soundings off" 

 Newfoundland, and Labrador, and Greenland, and by their 

 rate of flotation when they float with 300 feet above water, as 

 "flat-topped islands of ice" in southern seas. A "glacier" 

 cannot easily be measured on shore, but these vagrant fragments 

 roughly measure parent glaciers. A pressure of 3,000, or of 

 1,000, or of 500 feet of ice upon sand]or stone moving in an ice- 

 channel is great abrading force. At the base of every ice-fall, 

 or ice-rapid, the plunging ice-river must tend to " excavate," 

 because falls and rapids of water excavate pools of various size 

 proportioned to their power. The area of Greenland nearly 

 equals that of India, and that area, so far as it is known, is 

 covered with thick ice which is slowly moving seawards. The 

 coasts are furrowed by deep hollows, of which most contain 

 flowing glaciers, of which many enter the sea, and launch 

 "islands of ice." Some "bergs" now float to the lowest 

 latitude reached by northern drift-stones on shore in Europe and 

 in America. I say nothing here about marine glaciation. The 

 Greenland glaciers are flowing from an area where water generally 

 falls frozen ; they flow as rivers now flow from India, and all of 

 them are slowly wearing their channels at some rate, and working 

 up stream like Niagara Falls. There is no measure for the time 

 during which these powerful ice-rivers of Greenland have been 

 slowly hollowing stone by frequent flowing, unless it be the 

 work of erosion done. It is denied that the woik was done by 

 the glaciers. Yet no rivers flow where ice fills the dales, and 

 these Greenland dales have been " eroded," and bear " the usual 

 evidence of powerful ice erosion," according to photography and 

 descriptions. According to the clearest marks the whole Scandi- 

 navian peninsula, and the whole of Finland have at some time 

 been covered by ice on the scale of Greenland ice. Sermitualik 

 glacier, photographed by Mr. Bradford before 1870, is near 

 Cape Desolation in Greenland, opposite to Shetland, Bergen, 

 Christiania, St. Petersburg, &c. It is from three and a half to 

 four miles wide where it enters the sea, and there it is about 800 

 feet thick. It extends inland as far as the eye can reach, and 

 probably comes from the watershed of Greenland. Taking the 

 ice to weigh only 55 lbs. per foot cube, the pressure above the 

 sea-level on the ice channel is about 44,000 lbs. on the foot 

 square. Between ice and rock are large stones, grit, and mud ; 

 and the rock is rounded where it is visible at the edge of the 

 glacier, near the sea-level. The slopes between the lakes of 

 Finland, and the gulf near Viborg, at the side of the Saiamen 

 canal, and elsewhere, are polished, striated, and rounded. I 

 took rubbings in September, 1865, and recognised the work 

 of ice on the scale of Greenland ice. In Norway the old 

 marks are plain on the sides of firths and dales, and some lead 

 back to glaciers, which still flow from large areas upon the 

 watershed, which still are covered by considerable sheets of ice. 

 In Greenland this engine is seen at work ; in Scandinavia 

 the work of the engine is better seen. That work is, 

 first a rounded worn plateau about the v.atershed called 

 the " fjeld ;" second, a series of slopes much glaciated ; and 

 third, below these slopes, long grooves hollowed out of the 

 solid, called "dales." In these dales rivers now flow to lakes 

 and to firths. Of these nvers some have worn deep water- 

 courses, and canons proportioned to their size and age. At the 

 bottom of the dales are hollows which are called lakes, and firths 

 when they hold fresh or salt water ; in the rivers are smaller 



