20i 



KNOWLEDGE 



[November 1, 1893. 



although, fortunately, it has a prospect of surviving for 

 many years to come in the Sudan and Kordotan. The 

 great majority of the giraiies kUled at the present day in 

 southern Africa are shot solely for the sake of their skins, 

 which are now, owing to the practical extermination of 

 rhinoceroses south of the Zambesi, and the ever-increasing 

 scarcity of the hippopotamus, used in the manufacture of 

 the formidable South African whips known as jamhoks. 

 The value of a skin usually varies, according to size and 

 quality, from £2 10s. to £4, although they have been 

 known to fetch £5 apiece ; and it is for the sake of such 

 paltry sums that one of the noblest and most strange of 

 mammals stands in imminent danger of extermination ! 



We may conclude this notice by mentioning that although 

 the giraffe was familiar to the Romans of the time of the 

 empire, by whom it was known as the camelopard, it 

 appears to have been almost completely lost sight of in 

 Europe in later times till the closing decades of the 

 eighteenth century, although a single example is stated to 

 have been exhibited alive in Florence some four centuries 

 ago. With that exception, it seems to have been generally 

 regarded as a fabulous animal until one was shot near the 

 Orange River in 1777 by an Englishman, and another by 

 the French naturalist, Le Vaillant, in 1784. From that 

 time onwards our knowledge of the animal and its habits 

 gradually increased, although it was not till the spring of 

 1830 that four living specimens from the Sudan were 

 brought alive to London, where some of their descendants 

 lived continuously till 1892, since which date the species 

 has been unrepresented in the Regent's Park. 



THE MAKING OF MOUNTAIN CHAINS. 



By H. G. Wells, B.Sc. 



WITHIN the past decade, speculation upon the 

 process of mountain formation has attracted 

 a considerable amount of attention from 

 geologists. With increased stratigraphical 

 knowledge, it has been possible to trace the 

 successive stages in the life of an elevated region with 

 increased certainty, and a great and growing quantity of 

 collateral information has been collected upon volcanic 

 phenomena, earthquakes, the microscopic structure of 

 rocks, and the behaviour of viscous bodies underpressure. 

 The history of every mountain range seems to resolve 

 itself into the story of an incessant struggle between 

 hypogene and solar energy. From the moment the land 

 emerges from the sea the forces of denudation begm to 

 act upon it ; as the uphea\Tng powers win for a time, and 

 the land gradients increase, erosive action becomes more 

 and more efficient, the wedges of the frost come to aid the 

 wear of the rain as the snow-line is approached, and at last 

 the Titanic forces of elevation, the strength of the caryatid 

 giant, old Seismos, becomes exhausted, and the record of 

 his efforts is slowly erased by the at last triumphant 

 forces of the air. This, in brief, is the life-history of 

 every mountain chain, the common plot of all the stories 

 at which we are now to glance. 



Somewhere in Swedenborg's writings there is an account 

 of the examination by angels of one of the risen dead. 

 They did not ask the man questions, or subject him to 

 cross-examination. They simply took his body, and 

 methodically from that infallible document read out to him 

 all the things he had done. If I remember rightly, they 

 began by " unrolling his fingers." Whatever act his fingers 

 had performed had left its record in their structure, and 

 whatever thought had passed through his brain had made 

 its infinitesimal difference there. This is precisely the way 



the scientific man hopes at last to build up the history of 

 the past. Every hill, every pebble, every microscopic 

 patch in a weathered felspar, every cleavage crack in a 

 needle of hornblende, rightly interpreted, bears its witness 

 to the cosmic forces that have besn at work upon them ; 

 and at present we must read tlie story of the mountains in 

 this way, so far as our light permits. We may best begin 

 by remarking upon a few of the most significant features 

 of existing mountain masses. 



Perhaps, in the order of their importance, one should first 

 notice the fact that almost all our great mountain chains 

 have, high up upon their iianks, rocks of comparatively 

 recent origin, and that we often find great thicknesses of 

 such rocks. The very summit of Mont Blanc, for instance, 

 was once surmounted by -Jurassic rocks. Cretaceous rocks 

 crown the Rocky Mountains, and Tertiary masses lie at 

 great elevations upon their sides. Nummulitic limestone, 

 a foraminiferal rock of early Tertiary age, is found at 

 heights of nineteen and twenty thousand feet on the 

 Himalayas, and still younger Pliocene formations lie high 

 on their slopes. The elevated nwlassc of the Alps is a 

 middle Tertiarj' rock. Not one of the really great mountain 

 chains of the globe appears to have been elevated, or 

 indeed above water, during the Mesozoic period. At that 

 time each was an area of deposition, and further, of 

 subsidence, as the accumulated thickness of Meso/.oic 

 strata witnesses. So that we must figure for the beginning 

 of our story a sea, near land indeed, or strata would not 

 accumulate, and with a sinking bottom, or its silting up 

 must have ocoui'red in the place of continuous deposition. 



Of course, when we state that the early Tertiary and 

 upper Mesozoic rocks are recent, the non-geological reader 

 must understand we mean recent relatively to the length of 

 geological periods. The date of accumulation of these 

 sediments is certainly a matter of hundreds of thousands 

 if not of millions of years. 



Mr. Mellard Reade has insisted particularly upon the 

 importance of this fact of the comparatively modern 

 sedimentary structure of mountain masses. He has, 

 indeed, propounded a theory of the origin of mountain 

 elevation largely based upon this. As everybody knows, 

 there is within the earth an enormous store of heat ; for 

 instance, near the surface for every fifty feet or so we go 

 down the temperature rises 1°. The temperature of the 

 surface — disregarding solar radiation — is the net result of 

 two processes ; heat must be continually arriving from the 

 hotter interior by conduction, and heat must be continually 

 escaping by radiation into space. Mr. Reade asks us to 

 consider the result of a continually increasing thickness of 

 strata over any part of the earth's surface. It will act, 

 just as a blanket does, by preventing the escape of heat. 

 The rocks below will in time grow warmer, since they are 

 no longer superficial, and the growing accumulation of 

 strata will also be heated. The whole mass will expand 

 horizontally and vertically, the movement of subsidence 

 will finally cease, and at last, as a consequence of the 

 lateral strain, the horizontal strata will bulge and be 

 ridged upward into the form of mountain masses. 



More striking, perhaps, than the recent age of their 

 constituent strata, and almost equally significant, is the 

 folding that mountainous regions have undergone. We 

 cannot do better than call attention here to the acconii)auy- 

 ing figure of tliat classical example, Mont Blanc. The 

 strata the reader will see here have been folded and folded 

 again, and their ridges have been denuded. If one takes the 

 edges of a sutticiently flexible book and approximates the 

 ends, one may imitate these foldings roughly, but they may 

 be imitated still better by compressing layers of cloth 

 laterally beneath a weight. 



