Jan. 31, 1884] 



NATURE 



325 



THE ORIGIN OF THE SCENE R V OF THE 

 BRITISH /SLANDS' 

 '1"*HE insular position of Britain, which we are accu>tomed to 

 regard as an essential and aboriginal feature of the country, 

 is merely accidental, and has not always been maintained. The 

 intimate relationof Britain with the Continent is well shown by the 

 Admiralty charts. If the west of Europe were elevated 200ft. — 

 that is, the height of the London Monument — the Straits of Dover, 

 half of the North Sea, and a large part of the English Channel 

 would be turned into dry land. If the elevation extended to 600ft. 

 — that is, merely the united heights of St. Paul's and the Monu- 

 ment — the whole of the North Sea, the Baltic, and the English 

 Channel would become land. There would likewise be added 

 to the European area a belt of territory from 100 to 150 miles 

 broad, stretching to the west of Ireland and Scotland. A vast 

 plani would unite Britain to Denmark, Holland, and Belgium, 

 and would present two platforms, of which the more southerly 

 would stretch from what are now the Straits ot Dover northward 

 to the northern edge of the Dogger Bank. The steep declivity 

 separating the two plateaux is doubtless a prolongation of the 

 Jurassic and Cretaceous escarpments of Yorkshire. It is trenched 

 at either end by marked depressions, of which the western is a 

 magnificent valley through which the united waters of the Rhine 

 and Thames %\ ould flow between the Dogger Bank and the York- 

 shire cliffs. The eastern gap would allow the combined Elbe 

 and Weser to escape into the northern plain. Possibly all those 

 rivers would unite on that plain, but, in any case, they would fall 

 into a noble fjord which would then be revealed follouing the 

 southern coast line of Norway. Altogether an area more than 

 thrice that of Britain would be added to Europe. By a total ri e 

 of i,Soo feet, Britain would be united to the Faroe Islands and 

 Iceland ; while the Arctic and Atlantic Oceans would be separ- 

 ated. From its position on the oceanic border of a continent, 

 Britain has been exposed to a great variety of geological change. 

 Ill such a position marine erosion and deposit are most active, 

 and a slight upheaval or depression, which would have no senible 

 effect in the interior of a continent, malves all the difference 

 between land and water. Moreover, there appears to be a tend- 

 ency to special disturbance along the edge of an ocean. America 

 affords the most marked proofs of this tendency, but in the 

 structure of Scandinavia and its prolongation into .Scotland and 

 Ireland there appear to be traces of similar ancient ridging up 

 of the oceanic border of Europe. 



There is a remarkable cjnvergence of geological formations in 

 Britain, each carrying with it its characteristic scenery. The 

 rugged cr>'stalline rocks of Norway reappear in the Scottish 

 Highlands ; the fertile Chalk, with its smooth downs and gentle 

 escarpment, stretches across to us from the north of France ; 

 the great plains of North Germany, strewn with the debris of 

 the northern hills, extends into our eastern lowlands ; even the 

 volcanic plateaux of Iceland and Faroe are prolonged into the 

 Inner Hebrides and the north of Ireland. 



The present surface of Britain is the result of a long, compli- 

 cated process in which underground movements, though some- 

 times potent, have only operated occasionally, while superficial 

 erosion has been continuous, so long as any land has remained 

 above the sea. The order of appearance of the existing features 

 is not necessarily that of the chronological sequence of the rocks. 

 The oldest formations have all been buried under later accumula- 

 tions, and their re-emergence at the surface has only been brought 

 about after enormous denudation. In its general growth, Britain 

 like the rest of Europe has, on the whole, increased from the north 

 by successive additions along its southern border. The oldest 

 upheavals ridged up the Palaeozoic rocks into folds running north- 

 north-east and south-south-west, as may yet be seen in Scotland, 

 in the Lake Country, and in \Vales. By a later series of folds 

 the younger Palaeozoic rocks were thrown into north and south 

 and east and west ridges, the latter of which still powerfully 

 alTect the topography in southern Ireland, and thence through 

 .South Wales and Belgium. An east and west direction was 

 followed by the more important subsequent European disturb- 

 ances, such as those that upheaved the Pyrenees, Jura, and Alps. 

 Some of the latest movements that have powerfully affected the 

 development of our scenery were those that gave the Secondary 

 rocks their general tilt to south-east. It is very doubtfiU if any 

 irt of the existing topography can be satisfactorily traced back 

 ■eyond middle or older Tertiary time. The amount of erosion 



■ Abstract of the first of five lectures by Archibald Geikie, F, R. S.. Director- 

 * icneral of the Geological Survey, given at the Royal Institution, J.-Hnuary 29, 



of some of the hardest rocks of the country since that date has 

 been prodigious, as may be seen in the fragmentary condition of 

 the volcanic plateaux of ihe Inner Hebrides. 



The main topographical features of Britain may be arranged 

 as mountains, tablelands, valleys, and plains. All our moun- 

 tains are the effect of erosion on areas ofjland successively upheaved 

 above the sea. In the development of their forms, the general 

 outlines have been mainly determined by erosion independent 

 of geological structure ; while the details have been chiefly guided 

 by structure, but partially also by the rate [and kind of erosion, 

 Ruggedness, for example, has re.-ulted primarily from structure, 

 but has been aggravated by greater activity of erosion. The moun- 

 tainous west, with a greater rainfall and steeper slopes, is more 

 rugged than the mountainous east. The tablelands of Britain 

 are of two orders — i, those of deposit, which may be either (a) 

 of sedimentary rocks, horizontal or nearly so, as in the millstone 

 grit and Jurassic plateaux of Yorkshire, or (t>) of volcanic rocks, 

 as in the wide plateaux of Antrim, Mull, and Skye ; 2, those 

 of erosion, where, as the result of long-continued degradation, 

 a series of plicated rocks has been cut down into a more or less 

 uniformly level surface, as in South Wales. By the elevation of 

 such a surface into a high plateau, erosion begins anew, and the 

 plateau is eventually trenched into a system of ridges and 

 isolated hills, as has happened in the Highlands. The valleys 

 of Britain are the result of erosion either {a) guided by geological 

 structure, as in what are called longitudinal valleys, that is, 

 valleys which run along the strike or outcrop of formations, as 

 the Great Glen and Glen Spey in Scotland and the valleys of the 

 Trent and Avon in England; or (li) independent of geological 

 structure, as in the transverse valleys which embrace the great 

 majority of British examples. Our plains have been produced 

 by the spreading out of detritus by the operation of rain and 

 rivers, as in river terraces and alluvial plains ; by the sea, as 

 in raised beaches ; or by land-ice and floating-ice, as in the 

 glacial drifts of the Lowlands. The existing watershed of 

 Britain is profoundly significant, affording a kind of epitome of 

 the geological revolutions through which the surface of the 

 country has passed. It lies nearer the west than the east coast. 

 The western slope being thus the steeper, as well as the more 

 rainy, erosion must be greater on that side, and consequently 

 the watershed must be slowly moving eastward. Probably the 

 oldest part of the watershed is to be found in the Highlands, 

 where its ttend from north-north-east to south-south-west was 

 determined by the older Palaeozoic upheaval. Its continuity has 

 been interrupted by the dislocation of the Great Glen. After 

 quitting the Highlands it wanders across the Scottish Lowlands 

 and Southern Uplands, with no regard to the dominant geological 

 structure of these districts, as if, when its course was originally de- 

 termined, they had been buried under so vast a mass of superin- 

 cumbent rock that their structuredid not affect the surface. Running 

 down the Pennine Chain the watershed traverses a region of 

 enormous erosion, yet from its general coincidence w'ith the line 

 of the axis of elevation, we may perhaps infer that the anticline 

 of the Pennine Chain has never been lost under an overlying 

 sheet of later undisturbed rocks. The remarkable change in the 

 character of the watershed south of the Pennine Chain carries us 

 back to the time when the great plain of the Secondary rocks of 

 England was upraised with a gentle inclination to east and south- 

 east. The softer strata between the harder escarpment-forming 

 members of the Jur.assic series and the Paljeozoic rocks of the 

 Pennine Chain were worn away, and two rivers carrying off 

 the drainage of the southern end of that chain flowed in oppo- 

 site directions, the Avon turning south-west and the Trent north- 

 wards. By degrees these streams moved away across the 

 broadening plain of softer strata as the escarpments emerged 

 and retreated. At the same time streams collected the drainage 

 from the uprising slope of Secondary rocks and flowed south- 

 eastward. Successive lines of escarpment have since been 

 developed, and many minor watersheds have arisen, while the 

 early watershed has undergone much modification, these various 

 changes pointing to the continuous operation of running water. 



SOCIETIES AND ACADEMIES 



London 

 Royal Society, December 13, 1883. — "Experimental Re- 

 searches on the Electric Discharge with the Chloride of Silver 

 Battery." By Warren De La Rue, M.A., D.C.L., Ph.D., 

 F.R.S., and Hugo W. Muller, Ph.D., F.R.S. 



