« ПредыдущаяПродолжить »
drop into some treacherous pool. So nature deprived it of wings, and, instead, lengthened its antennæ, so that it could feel in time to save itself when, with less impetuous leaps, it came against an obstacle.
Do these changes also point to a great lapse of time? or may we believe that among the lower forms of life, and those in which the generations follow one another most rapidly, these changes also may be much more rapid ? There is nothing in the nature of the case to show that evolution must be slow. If forms of life are modified by their environment, the rate of change in the organic being may yet be slow; but, as far as we can see, it often is very rapid. What an opportunity for studying such questions. An animal, the type of liveliness—the sunny grasshopper, the flying ruby emerald or topaz—is plunged at once and for ever into the darkness of earth's innermost recesses. No need of wings, where it dare not fly; no use for eyes, where it cannot see; no advantage in gorgeous hue, where there is no light to be reflected. What will become of it? Nature cuts off its wings; nature blinds its eyes; nature washes out its brilliant colours; but, in compensation, gives it means to guard against its new dangers by lengthening out its antennæ, to let it feel its way about.
If this process is still going on, what will it come to? Does it go on indefinitely throughout all nature, or are there limits of evolution for all, or its own limit for each form? On the one hand, from analogy we learn that we must not assume, because development goes on constantly within our short experience, that it must go on in the same way indefinitely Were a being from a treeless planet to visit our earth and report upon what he observed of the growth of an oak, he might record that the tree developed in the same way each year-bud, leaf, flower, fruit; and that twig, branch, and bowl grew in proportion; and the roots shot out downwards and sideways, seeking, with what looked almost like intelligence, the best-suited soil. He saw ino reason why it might not go on for ever while our earth could bear it. How different the fact, The oak tree has its term of life. So may species, for aught we can at present certainly say, have their term of life. But what determines it? Again, I appeal to analogy not as an argument so much as in illustration. Fairy-rings on the grass are the annular spaces on which a certain fungus grows. This fungus scatters its spores all round, but they will grow only on the virgin soil outside, and, as they will not grow where they have grown before, inside the ring the species becomes extinct.
But plants help one another. A forest creeps along the hillside and the vale, destroys the life that will not grow below it, but itself exhausts the soil, and in time perishes, having, however, renovated the soil for other plants which were kept out so long. In the four and six course farming man recognises this. Many diseases are but growths which creep across the world, feeding upon the constitutions that favour them, and then die out. Could we but destroy the seed that lingers somewhere to spread again over an earth peopled by new generations.
Shall we say, then, this is the difference? The individual has a term of life measured by the vitality inherent in himself, which cannot be wholly renovated.
The species has no limit to its life, save that imposed by its surroundings, which, however, it renders unsuitable by using up that on which its life depends. This, however, can be renewed. But will the same life be there to take advantage of the renovation? That is the question in each case.
The dying-out and migration of species thus becomes only the outward growth of the fairy-ring.
The incoming of new species only the appearance of the wingless, colourless grasshopper in the Mammoth Cave.
The CHAIRMAN (H. Cadman Jones, Esq.).—I presume I need hardly put it to the Meeting that we should return our thanks to Professor Hughes for his very interesting paper, which it has been a great pleasure to listen to. After some communications have been read, it will be open to those whose studies have lain especially in the direction of the subject taken up to commence the discussion.
Captain FRANCIS PETRIE, F.G.S. (the Honorary Secretary). Among the letters received from those unable to be present this evening are the following. The first and second are from the Duke of Argyll and Professor Hulke, F.R.S., mentioning that they have read Professor Hughes's paper with much interest, and adding that they have no criticisms to pass
The third is from Sir J. William Dawson, K.C.M.G., F.R.S. :
“McGill College, Montreal,
“ March 16, 1887. “I beg to thank you for your kind communication of an early copy of the interesting paper by my friend, Professor McKenny Hughes, on Caves. I am glad that Professor McKenny Hughes is applying his well-known acuteness and discrimination to those inodern deposits which have given rise to so much somewhat crude discussion and speculation. His paper on the Drifts of the Vale of Clwyd * I regard as one of the most valuable we have recently
* Quarterly Journal of the Geological Society, February, 1887.
had, and especially so as placing the drifts of Wales more closely in relation with those so widely distributed in Canada, than heretofore. In the present paper he has very clearly illustrated, in the case of Ingleborough Cave, the fact that true uniformitarianism in geology includes local and occasional catastrophic action. This I regard as of the most vital importance to geological reasoning, and especially in the explanation of cavern deposits and river gravels, which, niore than most other formations, are liable to be affected by violent and paroxysmal local debacles, as well as by apparently capricious accidental changes. The utmost caution and the most careful and minute observation are necessary in dealing with these deposits, and in estimating their ages and their relation to the human period.
"With kind regards,
" J. WILLIAM DAWSON." “Captain Francis Petrie."
The Rev. J. Magens Mello, M.A., F.G.S., writes :
“I am very sorry that I am unable to be present at the reading of Professor McKenny Hughes's paper this evening. To the greater part of it I have nothing that I could add save in the way of corroboration from personal observations of similar instances. But I have the very strongest doubts whether there can be any trace whatever left in our caves of the Noachian Deluge, even granting that catastrophe involved our islands, which I am hardly prepared to admit. My own experience of British caves, both from observation and from reading, tends to show that the contents of, at any rate, most of them have been the gradual accumulation of a long series of years, during which they were occupied partly by beasts, partly by nien, and that there is no evidence whatever to be found in them of so sudden a cataclysm as the Great Flood, the historical character of which is, however, abundantly confirined by overwhelming proofs of various kinds.”
The Rev. Dr. Walker, F.L.S., says :
“Dun Mallard, Cricklewood,
“ February 19.
“On p. 96, Professor McKenny Hughes speaks of the appearance of the wingless, colourless grasshopper in the mammoth cave.' I should be glad to be informed whether or not the same species, winged and coloured, is found outside the caves in broad daylight ? If not, the inference would seem to be that the grasshopper in question had originally been created sightless, to fit it for its natural surroundings, and not have gradually become so through the unused organ being atrophied and lost. As it is inconceivable that any particular species would survive in the dark cave, and have disappeared long years since in the open air, where all the conditions for supporting and prolonging existence are so much more favourable. Lastly, short antenne and the possession of wings are not the characteristics of all grasshoppers living in the light, as I can prove by species captured by myself and in my own collection."
Also a letter, just received, from Sir Charles Warren, regretting that he is unable to be present, as he had intended.
Sir WARINGTON W. SMYTH, F.R.S.-In response, sir, to your invitation, I have much pleasure in saying that I am sure the paper we have just listened to must have been a great treat to the whole of us. My friend, Mr. McKenny Hughes, the Woodwardian Professor of Geology at Cambridge, has had an unusual amount of experience in hunting up and examining caves, and I may state that, having during a series of years had opportunities of exploring several of those he has mentioned, I feel particularly indebted to him for the graphic account he has given us of a district and cave I have not seen.
I shall not attempt to follow him into the difficult region into which he has been carried by the wingless grasshoppers of which he has spoken,—a part of the question which we may look upon as separated from the earlier portion of the paper.
I desire only to express to him the reasons why I feel especially gratified with some of the points he has put before us in describing the modes by which caves have been formed and the manner in which they have been filled by various kinds of material. I recollect that in my earlier days of geological study I was surprised to find that a former generation of geologists—I speak especially of Professors Buckland and Sedgwick and their continental contemporaries – set very great store by the examination of caverns, and entered not only into a series of explorations, but of philosophic considerations, of a inost interesting character, on this subject. Indeed, I do not know that anything more interesting can be pointed out than the work by Professor Buckland, of which Professor Hughes has reminded us -- Reliquire Diluviano,—although it is, doubtless, true that the theory on which he relied so much at the time he wrote that book is now very much discredited. The descriptions he gave with such admirable freshness of the different caves he visited and the facts he submitted cannot be studied by us without great advantage. I had the happiness, when a young man, of making a tour into that part of Franconia in which Dr. Buckland particularly delighted, and of seeing some caves in the neighbourhood of Muggendorf, which he made a special locality; and the impression formed in my mind coincided with his view as to the filling of the caverns in that part of the world by a succession of cave bears with the bones of animals which they had dragged in, so that in process of time they became a rich harvest to the geologist, who, on taking up the stalagmite which covered the cavern floors, found the bones of those animals embedded in it. I remember being greatly struck with a cave high up the side of the Muggendorf Valley, where it was clear that the hollow had been formed by the action of water containing carbonic acid, and that some of the bones discovered there must have come in by accident from openings above. In fact, the bones of two human beings were found in that cave underneath the chasm through which they had evidently fallen. The same thing has been impressed on me most forcibly in the district of Cross Fell, Cumberland, where, having, some few years ago, had occasion to be frequently crossing the mountains, it happened that, being short of time, I was sometimes so pressed that, after I had left the railway at Penrith, in making my way over a place 1,000 feet high to my shooting-box on the middle of the moor, I was overtaken by darkness before I could reach home. I had observed how amenable the district was to swallow holes. Very often, where there was only a thin covering of sandy rock, there was, at short distances from one another, a succession of caverns hollowed out of the limestone stratum, and these becoming enlarged had given way at the top and fallen in so as to leave a crater-like opening. One night, when it was pitch dark, I came suddenly upon one of these craters, and tumbling head over heels picked myself up at the bottom. I then found that I was very near a little hole through which water was trickling, and when I got to the shooting-box I found, on putting my hands in my pockets, that they were full of moss ; so that I felt sure I had had a complete capsize. It struck me that, supposing I had broken my legs and had been left there to starve to death, my bones would probably have been carried by the water through one of the openings in the rock into a limestone cavern beneath. Thus it seemed to me that at times small bones may have been introduced into caverns through these openings above, and at others, bones of the larger animals may have got in through the chasms, we find in the rocks. There is the Plymouth limestone again, which often, through quarrying operations, has been the means of presenting to us the bones of lions and tigers and a number of other animals which at the present day are strangers to anything like our latitudes ; but I will not detain you by going into this branch of the subject. I may say, however, that what has been put before us in reference to the Ingleborough and other caves teaches us a very important lesson. rather astonished by what the author of the paper told us as to the stalagmitic floors being forced up by the action of a very beavy flood of rain water, and cannot help seeing therein one of those difficulties that are exceedingly apt to puzzle tyros in geological inquiry. I have always felt that the examination of these caves ought to be conducted with the very greatest care and caution, and that the question of their formation and contents was a matter requiring to be dealt with by the most experienced geologists ; because, when we come to the breaking up of stalagmite floors and the bories embedded in them, it stands to reason that conclusions of the most dangerous kind may easily be arrived at far too hastily. Whether one refers to caves that are to be found on the sea-shore or to caverns met with in the inland limestone districts, there are on all sides a great many subjects to be considered in forming our conclusions. I cannot help referring to one peculiarity in regard to caves, which, perhaps, Professor Hughes has not seen, but which 1 have noticed in a district to the east of Ingleborough, namely, at Swaledale, in the locality of Grinton Moor, where one finds on going through the caves the joints in some of the beds are enlarged in a curious fashion. The caves there, where the miners find the most valuable lead ores, are longitudinal, and present appearances so numerous, and so