436 



NATURE 



[Sept. 14, 1876 



ment between the two groups, the coincidence of their outlines, 

 and of the way in which they had been cut and carved ; but the 

 admirable researches of Mr. Judd have, in 1874, brought one 

 little fact to light which speaks volumes for the enormous changes 

 which must have taken place since the volcanoes of the Miocene 

 over a portion at least of the Highland area, and which may 

 therefore have taken place over the whole of it. The land upon 

 which the Miocene vegetation flourished and upon which the lava 

 streams of the volcanoes were poured out, seems to have been for 

 the most part a land consisting of Cretaceous and Secondary 

 rocks. The fragments of that country which remain are gener- 

 ally consistent with the supposition that they were deposited in 

 a sea which washed round the bases of the Highland mountains, 

 but which never covered them. 



Like the fragments of the Old Red Sandstone, the remains of 

 the Secondary rocks lie along the margins and fringes of the 

 Silurian hills ; but Mr. Judd has made the startling discovery of 

 an outlier of the whole series of the Secondary rocks, including 

 representative beds of the Trias, Lias, Green Sand, and Chalk, 

 together with deposits, probably lacustrine — all lying on the top of 

 one of the mountains of metamorphic gneiss which constitute the 

 district of Morven. This fragment has been preserved by having 

 been covered by a sheet of lava from some great neighbouring 

 volcanic centre, the position of which is indicated by Ben 

 More in Mull ; but the mass of volcanic trap which was covered 

 up and preserved this relic of the Cretaceous land is itself a frag- 

 ment occupying the top of a mountain of gneiss separated from 

 the remainder of the sheet of lava to which it belongs by deep 

 valleys precisely similar to those which divide the hills from each 

 other throughout the whole area of the Highlands. The position 

 of an outlier of the Cretaceous rocks on the summit of a moun- 

 tain of gneiss is rendered still more curious by the circumstance 

 that in that position the beds are not tilted, or in any way 

 apparently disturbed. They are arranged horizontally, as if the 

 ocean floor on which they were deposited had occupied that level, 

 or as if its deposits liad been lifted up over so large an area that 

 any small section of that area could retain its original horizon- 

 tality. The lower Silurian gneiss beds on which these Secondary 

 deposits have been laid are violently twisted and contorted, and 

 this structure must have belonged to them when they constituted 

 the floor of the Cretaceous sea ; the position of the Miocene 

 basalts capping the Secondary deposits proves that the whole 

 mountain, as a mountain, is of later date than the Miocene age 

 — how much later we cannot tell, and thus that the causes of geo- 

 logical change which have cut up the country into its present form, 

 though they doubtless began in very remote epochs, have at least 

 been prolonged into a comparatively late age in the history of 

 the globe. 



It would, I think, be aff'ectation to pretend that our science 

 enables us to follow with anything like distinctness of conception 

 the exact nature and sequence of operations which through 

 such a vast lapse of time have brought about the final result, but 

 1 believe in something like the following outline of events : — 



First, that subsequent not only to the consolidation, but pro- 

 bably also to the metamorphism of the Lower Silurian deposits, 

 the whole area of the Western and Central Highlands became an 

 area of that kind of disturbance which arose from lateral pressure, 

 due to secular cooling, and consequent contraction and subsidence 

 of the crust of the earth. Second, that the crumpling, contortion, 

 and tilting of the Silurian beds which we now see, arose from 

 that disturbance. Thirdly, that then were determined those 

 great general lines of strike running from south-east to north- 

 west which are to this day a prominent feature in the physical 

 geography of the country. Fourthly, that during that period of 

 disturbance, and as part of the movement which then took place, 

 the disturbed rocks fell inwards upon materials at a great heat, 

 which rose in a pasty state along lines ol least resistance, 

 and thus came to occupy various positions sometimes inter- 

 calated among the sedimentary beds. Fifthly, that to this 

 period, and to this method of protrusion, we owe some at least 

 of the measures of granitic material which are abundant in the 

 Highlands in particular ; that to this period belongs the porphy- 

 ritic granites on the north shores of Loch Fyne. Sixthly, that 

 during the later ages of the Palseozoic period volcanic action 

 broke out at various points, accompanied by great displacement 

 and dislocation of strata, and that to this, witli the utnudation 

 which followed, we owe much of the very peculiar scenery of 

 the south-western coasts, especially in the district of Lome, in 

 Argyllshire. Seventh, that we have no prooi that the Central 

 Higtdands were ever under the seas which laid down the deposits 

 of the later Palaeozoic age. Eighth, that such evidence as we 



have, points rather to the conclusion that they were not under 

 such seas, since such fragments as remain of the Old Red and of 

 the Carboniferous rocks appear to have been deposited round the 

 bases and in the marginal hollows of the Silurian hills. Ninth, 

 that, in like manner, we have no evidence that the great mass of 

 the Central or Western Highlands were ever under the seas of 

 the Secondary ages, which, on the contrary, appear to have 

 deposited their sediment upon an area outside of, but probably 

 surrounding, the area of these Central Highlands, and certainly 

 upon those north-eastern and western flanks. Tenth, that the 

 whole area of the Inngr Hebrides and of the water dividing them, 

 together with some portion of the mainland, as in Morven, was 

 an area occupied by Secondary rocks. Eleventh, that in the 

 Tertiary ages — probably in the Eocene and certainly in the Mio- 

 cene — those rocks formed the bases of a great land of unknown 

 extent, very probably extending for a great distance both to the 

 east and west of the present coasts of Scotland and embracing 

 the north of Ireland, Tweltih, that this country became in tlie 

 Miocene age, and possibly earlier, the scene of great volcanic 

 outbursts, which covered it with vast sheets of lava and broke 

 up its Sedimentary rocks with every form of intrusive plutonic 

 matter. Thirteenth, that later in the Tertiary periods and per- 

 haps as late as the Pleiocene, this volcanic country was itself 

 broken up by immense subsidences and upheavals, giving both 

 occasion and direction to the agencies of denudation and to 

 enormous removal of material. Fourteenth, that this Tertiary 

 country had been thtis broken up and nothing but its fragments 

 left when the glacial epoch began, and that the main outlines of 

 the country as we now see it had been already determined when 

 glacial conditions were established. Fifteenth, that thus the 

 work of the glacial period has been simply to degrade and 

 denude pre-existing hills and to deepen pre-existing valleys. 

 Sixteenth, that during the glacial epoch there was a subsidence 

 ot land to the depth of at least 2,000 feet above the level oi the 

 present sea, and again a re-elevation of the land to its present 

 level. Seventeenth, that this re-elevation has not restored the 

 land to the level it ttood at before the subsidence began ; but 

 has stopped greatly short of it, and that the deep arms of the 

 sea, or lochs, which intersect the country and some of the 

 deeper fresh-water lakes, such as Loch Lomond, are the valleys 

 still submerged which at the beginning of the glacial epoch were 

 high above the sea and furrowed in flanks of loftier mountains ; 

 that during the glacial period the work of denudation and degra- 

 dation was done, and done only, by ice in the three well-known 

 forms — first, of true glaciers.descending mountain slopes ; second, 

 ot icebergs detached Irom the termination of these glaciers where 

 they reached the sea ; and third, by floe or surface ice driven by 

 currents which were determined in direction by the changing 

 contours of the land during the processes of submersion and re- 

 elevation. 



It would be impossible on this occasion to illustrate or support 

 these various propositions by going into the evidences on which 

 they rest ; but as those of them which relate to the operations of 

 the glacial epoch express a decided opinion upon questiorrs now 

 involving much disptite, 1 must say a lew words in explanation or 

 defence of that opinion. 



It will be seen that I disbelieve altogether in this theory of 

 what is called an ice-cap, or, in other words, I hold that there is 

 no evidence that there ever existed any universal mantle ot ice 

 higher or deCf^er than all the existing mountains, covering them 

 and moving over them from distant western regions. 



In the first place, this theory presupposes conaitions of climate 

 which must have prevailed universally over the whole northern 

 hemisphere, whereas over a great portion of that hemisphere, 

 west 01 a certain meridian on the American continent, all traces 

 of general glaciation and of any gencial distribuiion of erraiics 

 disappear. In the second place, tnc theory assumes ttiat masses 

 of ice lying upon the surface 01 the earth more than mountain 

 deep, would have a proper motion of its own capable of 

 overcoming the friction not only of rough level surfaces, 

 but even of the steepest gradients, for which motion no 

 adequate cause has been assigned and which has never been 

 proved to be the natural consequence of any known force 

 as to be consistent with the physic<d properties of the material 

 on which it is supposed to have acted. In the third place, as a 

 matter of lact, there does not now exist anywhere on the globe 

 masses of ice which can tie proved to have any motion of this 

 kind or to be sutjject to forces capable ol driving and propelling 

 it in the manner and with the eflects which the theory asaumcs. 

 The case of Greenland, which is often referred to as an example, 

 does not present phenomena at all similar to those attributed to 



