teb. 7, 1884] 



NA TURE 



347 



goes from Novaya Zemlya over to Spitzbergen, availing himself 

 of the archipelagos scattered between the two islands? 



In Nos. 9 and 10 of vol. x. of the Transactions oj the Berlin Geo- 

 sraphical Society, is an address on thewild tribes of Madagascar, 

 by Herr T. Audebert, who divides them collectively, both those 

 of Malayan (the Hovas) and those of African descent, accord- 

 ing to their mode of life, into three classes : the inhabitants (1) of 

 the coast ; (2) of the woods ; (3) of the grassy lands and steppe-like 

 wastes of the southern interior. Of all the races the Sakalavi 

 are first in point of number, power, and civilisation. The 

 aborigines, or Malaga-y proper, are generally of a dark com- 

 plexion, though those of direct Arabian descent are very clear- 

 skinned, with hard features, broad, often also high forehead, eyes 

 wide apart, nose flat, lips prominent, but not swollen, mouth 

 broad, with splendid teeth. The long rather woolly hair is worn 

 in innumeraVjle plaits woven, in the case of the women, into 

 crowns, vaccine ears, snail-shells, &c., smeared with tallow and 

 ashes into the hardne^s of stone, and very malodorous. In the 

 grassy interior cattle-rearing is the principal industry ; on the 

 coast' fishing and the cultivation of rice. In the woods the 

 people live on roots, tubercles, and honey. — Next follows an 

 interesting though brief account of Dr. Stecker's chequered 

 travels, of nearly three years' duration, through Abyssinia. About 

 the middle of February, 1881, when Dr. Rohlfs left Debra 

 Tabor, Dr. Sleeker made his way to the Tana I-ake, which 

 he travelled round, sending a detailed map of it, executed 

 on the spot, to the German African Society. At Zabul, 

 the recently-acquired seat of King John, Dr. Stecker drew a 

 plan of the' grand and interesting chain of mountains traversing 

 the eastern part of Abys^ii ia, but both report and map failed to 

 reach the German Afr'ican Society, whither they were directed. 

 Dr. Stecker was bent on penetrating into Koffa, but en account 

 of war tumults and King John's refusal to give him permission, 

 was obliged to abandon his design. He, however, joined the 

 three kin^js. King John, the King of Slioa, and the Negus 

 Tekla Ilamianot into the Eastern Gala lands of Komboltsha, 

 Antsharo, Tshaffa, Rikke, and Argobba, and was thus enabled 

 to make first acquaintance with a tract of country never before 

 trodden by a European. — Some interesting particulars of travels 

 in South America are taken from a letter of Dr. G. Steinman 

 to Dr. W. Reiss, dated November 5, 18S3.— The stones col- 

 lected by Herr P. Gii^sfeldt on the north-west slopes of Acon- 

 cagua, at a height of from 55CO to 61CO metres have been 

 analysed by Prof. J. Roth of the Academy of Sciences, and the 

 result has established beyond all further doubt the fact that 

 Aconcagua is a volcano. 



THE ORIGIN OF THE SCENER V OF THE 

 BRITISH I SLA NDS ' 

 A TRUE mountain chain is the result of a local plication of 

 ■**• the earth's crast, and its external form, in spite of some- 

 times enormous denudation, bears a close relation to the contours 

 produced by the origmal uplift. Tried by this standard, hardly 

 any of the heights of Britain deserve the name of mountains. 

 With some notalile exceptions in the south of Ireland, they are 

 due not to local but to general upheavals, and their outlines 

 have little or no connection with those due to underground 

 movement, but have been carved out of uplieaved areas of un- 

 known form l>y the various forces of erosion. In the course of 

 their denudation the nature of these component rocks has ma- 

 terially influenced the elaboration of their contours, each well- 

 marked type of rock having its own characteristic variety of 

 mountain forms. The relative antiquity of our mountains must 

 be decided not necessarily by the geological age of their com- 

 ponent materials, but by the date of their upheaval or of their 

 exposure by denudation. In many cases they cm be shown to 

 be the result of more than one uplift. The Malvern Hills, for 

 exam|)le, which from their dignity of outline better deserve the 

 name of mountains than many higher eminences, bear internal 

 evidence of having been upheaved during at least four widely 

 serarated geological periods, the eailiest movement dating from 

 before the lime of the Upper Cambrian, the latest coming down 

 to some epoch later probably than the Jurassic period. The 

 oldest mountain fragments in Britain are those of the Archaean 

 rocks, and of these the largest portions occur in the north-west 



' .abstract of second lecture given at tl 

 by Archibald Geikie. F.R.S., Director-G 

 0>ntinued from p. 325. 



Royal Institution. February 5, 

 eral of the Geological Survey. 



of Scotland. Most of our mountains, however, belong to up- 

 heavals dating from Palseozoic time, though the actual exposure 

 and shaping of them into their present forms must be referred to 

 a far later period. Two leading epochs of movement in Paleo- 

 zoic time can be recognized. Of these the older, dating from 

 before the Lower Old Red Sandstone and part at least of the 

 Upper Silurian period, was distinguished by the plication of the 

 rocks in a d.jminant north-east and south-west direction, and the 

 effects of the e movements can be traced in the trend of the 

 Lower Silurian ridges and hollows to the present day. In Wales 

 two types of mountain-form exist — the !-'nowdon type, and that 

 of the Breconshire Beacons. In the former the greater promin- 

 ence of the high grounds arises primarily from the existence of 

 masses of volcanic rocks, which from their superior durability 

 have been better able to withstand the progress of degradation. 

 In the latter the heights are merely the remaining fragments of a 

 once continuous tableland. The Lake District presents a re- 

 markable radiation of valleys from a central mass of high 

 ground. It might be supposed that these valleys have been 

 determined by some radiating system of fractures in the rocks ; 

 but an examination of the area shows them to be singulai^ly inde- 

 pendent of geological structure. So entirely do they disregard 

 the strike, alternations, and dislocations of the rocks among 

 which they lie that the conclusion is forced upon us that they 

 have beeri determined by some cause wholly independent of 

 structure, and before the present visible stracture was exposed at 

 or could affect the surface. Tliis could only have happened by 

 the spread of a deep cover of later rocks over the site of the 

 Lake mountains. The former presence of such a cover, which 

 is demanded for the explanation of the valleys, can be inferred 

 from other evidence. The Carboniferous Limestone on the 

 flanks of the Lake District is so thick that it must have 

 spread nearly or entirely over the site of the mountains. 

 But it was overlaid by the Millstone Grit and Coal-measures 

 so that the whole area was probably buried under several 

 thousand feet of CarbDniferous strata which stretched con- 

 tinuously across what is now the north of England. At the 

 time of the formation of the anticlinal fold of the Pennine Chain 

 the site of the Lake District appears to have been upraised as a 

 dome-shaped eminence, the summit of which lay over the tract 

 now occupied by the heights from Scafell to Helvellyn. The 

 earliest rain that fell upon this eminence would gather into 

 divergent streains from the central watershed. In the course of 

 ages, after possibly repeated uplifts, these streams have cut down 

 into the underlying core of old Palaeozoic rocks, retaining on 

 the whole their original trend. Meanwhile the whole of the 

 overlying mantle of later formations has been stripped from the 

 dome, and is now found only along the borders of the moun- 

 tains. The older rocks yielding to erosion, each in its own way, 

 have gradually assumed that picturesquentss of detail for which 

 the area is so deservedly famous. The Scottish Highlands like- 

 wise received their initial plications during older Palaeozoic times 

 their component rocks having been thrown into sharp fold, 

 trending in a general north-east and soutli-west direction. But 

 there is reason to believe that they were in large measure buried 

 under Old Red Sandstone, and possibly under later accumula- 

 tions. No positive evidence exists as to the condition of this 

 region during the vast interval between the Old Red Sandstone 

 and the older Secondary rocks. We can hardly believe it to 

 have remained as land dm'ing all that time, otherwise, the 

 denudation, vast as it is, would probably have been still greater. 

 Not improb.ably the region had become stationary at a base-level 

 of erosion beneath the sea ; that is, it lay too low to be effectively 

 abraded by breaker-action, and too high to become the site of 

 any important geological formation. The present ridges and 

 valleys of the Highlands are entirely the work of erosion. When 

 they began to be traced the area must have presented the aspect 

 of a wide undulating tableland. Since that early time the valleys 

 have sunk deeper and deeper into the framework of the laud, the 

 ridges have grown narrower, and the mountains have arisen, not 

 by upheaval from below, but Ijy the carving away of the rest of 

 the block of which they formed a part. In this evolution, geo- 

 logical structure has played ati important part in guiding the 

 erosive tool-. The composition of the rock-masses has likewise 

 been effective in determining the individuality of mountain-forms. 

 The mountains of Ireland are distributed in scattered groups 

 round the great central plain, and belong to at least three geo- 

 logical periods. The oldest groups probably took their rise at 

 the time of the older Palaeozoic upheaval, those of the north- 

 west being a continuation of the Scottish Highlands, and those 



