458 



NATURE 



[March 9, 1893 



and eocene ; the lake of Geneva on the north side is miocene 

 or Jurassic ; the lake of Neuchatel, miocene ; lakes Thun and 

 Brienz, eocene or Jurassic ; lake Lucerne, eocene and miocene ; 

 lakes Zug and Zurich in miocene ; lake Constance miocene ; 

 lake Maggiore is mostly in gneis-^, but it is very sugs^estive 

 that it is here comparatively shallow, but becomes suddenly 

 deeper and reaches its maximum depth in its lower portion 

 where it is bordered on the east by the Jurassic beds; lake 

 Como also has its greatest depth in tiiassic rocks, the upper 

 portion, where gneiss prevails, deepening gradually southward 

 as in a submerged valley. Equally suggestive is the fact that in 

 the eastern Alps of Tyrol and Carinthia, where gneiss, porphyry, 

 and the older stratified rocks prevail, and where glaciers are not 

 now so extensive, there are hardly any lakes, except on the 

 northern borders, where a considerable number occur in eocene, 

 cretaceous, Jurassic, or triassic formations, 



These various facts as to the distribution of alpine lakes— 

 their almost total absence in all parts of the world outside of 

 glaciated districts, and within glaciated districts their prevalence 

 in the newer and more easily denuded rocks — are what have to 

 be explained by the advocates of the theory of earth-movements, 

 and this, so far as I am aware, they have never attempted to do. 

 Equally important, and equally difficult to explain on the earth- 

 movement theiry, is the fact that alpine lakes are almost always 

 situated just at those spots where, by means of converging 

 valleys, the glaciers would become heaped up and attain 

 their maximum thickness, or where there is good evidence that 

 they have been very thick ; and it is the grinding power of this 

 enormous weight of ice, acting differentially as regards the softer 

 and harder rocks, that has worn out hollows in pre-existing 

 valleys now occupied by lakes. In almost every case, too, it 

 will be seen that there is a constriction or narrowing of the 

 valley towards or beyond the lower end of the lake, which, by 

 preventing the free escape of the ice, has increased its thickness 

 and grinding power. 



In the presence of such important series of facts as those here 

 referred to, mere opinions, or even small and detailed cases of 

 difficulty, can have no weight ; but there is yet another considera- 

 tion, which most geologists will admit is antagonistic to the 

 earth-movement theory. The whole tendency of geological 

 observation is in favour of the usually very slow rate of earth- 

 movements, while it is equally in favour of the comparatively 

 rapid action of denudation by running water. But in order that 

 earth-movement could form a lake, it would be necessary that 

 the rate of elevation or depression should be so great that the 

 river could not keep pace with it by cutting down its channel ; 

 and, considering that all the rivers in question are rapid moun- 

 tain streams carrying great quantities of sediment, this will be 

 admitted to be a very improbable supposition. But when we 

 add to this the still greater improbability that such rapid eai'th 

 movements have occurred in scores and hundreds of cases, all 

 at about the same time, geologically speaking, and all just in 

 those spots where it can be shown that daring the glacial period 

 ice must have accumulated, and where the rocks were of such a 

 character as .to admit of being ground away ; and yet further, 

 that no similar earth movements producing similar results have 

 recently occurred in any part of the globe beyond the limits of 

 glaciation, the whole assumption becomes so hugely improbable 

 as to render the theory of lake-formation by ice-grinding easy in 

 comparison. 



Sir Charles Lyell considered that the gravest objection to the 

 glacial-erosion theory was the entire absence of lakes where 

 they ought apparently to exist ; and he instanced the valley of 

 Aosta and the Dora Baltea, the glacier of which produced the 

 enormous moraines of Ivrea. The valley of the Rhone above 

 Martigny may be adduced as another example of the 

 absence of lakes where they might he expected. But this 

 kind of difficulty will apply to many other valleys, and can only 

 be answered by general considerations. In both these cases the 

 valleys are comparatively broad and open, and have a rather 

 rapid descent. It is probable, therefore, that the ancient glacier 

 in both was of a nearly uniform thickness, so that its wear- 

 ing action on the floor of the valley would be tolerably 

 uniform. To produce a lake we require essentially a dif- 

 ferential action. There must be much more rapid 

 degradation in one part than in another, due either 

 to greater ice-accumulation or to softer rocks in one part 

 than in another. In both the valleys referred to there is much 

 uniformity in the rock-formations throughout, and even if some 

 lakes or chains of lakes had been formed, the enormous amount 



NO. 12 19, VOL. 47] 



of debris still brought down may well have filled up and alto - 

 gether obliterated them. The absence of lakes in certain valleyS 

 cannot be considered an argument of any value until it is 

 ascertained by borings that none have been formed and filled up 

 again. It must also be shown that the whole conditions are 

 such as to produce that amount of differential grinding down, 

 without which no lake can be expected to have been formed. 



It certainly seems to me that all the facts, all the probabilities, 

 all the converging lines of evidence, are in favour of the glacial 

 theory, to which the only serious objection is the assumption 

 that glaciers cannot move uphill. But that they can do so, and 

 have done so, is now admitted by most students of glacier- 

 motion, Mr. Jamieson, and other Scotch geologists, have 

 proved that glaciers, over 2000 feet thick, have travelled up 

 lateral valleys, and up the slopes of many hills and mountains ; 

 and when we consider that the Rhone glacier was 5000 feet 

 thick just above the lake of Geneva, and more than 2000 feet 

 thick where it abutted against the Jura, we can have no difficulty 

 in admitting that it might have travelled up the very gentle 

 slope of the lake bottom, which appears to be less than 100 feet 

 in a mile in its steepest parts. Alfred R. Wallace. 



Waves as a Motive Power. 



Having frequently observed the swimming motions of the 

 fishes in our Aquarium — and occasionally of porpoises in the 

 open sea — I have tried to make use for propelling boats of the 

 same principle of locomotion, as exemplified particularly in the 

 tail-fin. 



I fixed a fin (blade) of elastic material like a helm to the end 

 of a canoe ; moving that fin laterally to and fro, the same went 

 forwards. I have since learned that this "motor "was used 

 already twenty-five to thirty years ago by Ciotti, a Sicilian ; it is 

 of course only an exact version of the method of sculling with 

 one oar, familiar to all boatmen. Whilst trying my canoe and 

 models of boats I soon became convinced that a boat ought to 

 move forward if elastic fins are fixed to it, directed backwards, 

 in such a manner that their flat sides are pressed against 

 the surrounding water, when the boat rolls and pitches. The 

 elastic fins, whilst overcoming the resistance of the water, 

 curve like the fins of a fish, driving the water backwards and 

 consequently pushing the boat forwards. 



The canoe was provided with two horizontal fins at the stern, 

 and two vertical ones at the keel, total surface o'2 square 

 metres ; speed against rather sharp wind and waves estimated 

 at 25 metres per minute. I was unable to take exact measure- 

 ments, as the canoe was accidentally sunk before the experiment 

 was complete. 



I then provided another boat, three metres long, at each of 

 the two pointed ends with a horizontal fin (later on two), 

 and at the keel with two vertical fins ; these were all made of 

 steel sheet, i-o"8 mm. thick, subsequently replaced with 

 aluminium bronze. The boat covered, against a gentle sea and 

 wind, the distance of 900 metres in 25 minutes. Putting the 

 fins obliquely the boat turned towards the right or left ; directing 

 one group of the fins forward, and another of equal surface 

 backward, their action was paralysed, and in similar manner 

 it was easy to make the boat turn round on the spot or to move 

 backward. 



The changing of the surface of the fins (o'3 to o"6 square 

 metres) caused very little difference in the speed produced. 

 The same movements of the boat take place if the rocking is 

 caused artificially. 



I undertook a series of trials, in which I wish to acknowledge 

 with thanks the kind assistance of Mr. Nelson Foley. The first 

 result was that the rolling yields so little power, (very little 

 energy being sufficient to prevent rolling,) that the vertical fins 

 as a source of power may be nearly neglected in the calcula- 

 tions. 



As \.o pitching, the power resulting from the action of the 

 waves against gravity is proportioned to (weight of boat with 

 crew) X (number of undulations) x (height of waves). But only a 

 small portion of the energy developed in moving the boat up 

 and down acts upon the fins (surface of boat in water-line three 

 square metres, surface offinso'3 to o"6 square metres), and of 

 this remaining available force a considerable portion is lost by 

 the low efficiency of the fins. Supposing, for the sake of argu- 

 ment, the efficiency to be 25 per cent., the propelling capacity 

 in a moderate sea works out to the fraction of a man's power. 



Considering these circumstances it seems doubtful, even with 



