February 1, 1808. 



KNOWLEDGE 



27 



If doubt hangs round these masssB, which were once 

 thought to be ribs of the primordial earth, but which 

 appear to be often of very modern origin, we may look with 

 more respect upon the fundamental rocks exposed in broader 

 areas. Scandinavia and the north of North America have 

 already been referred to ; but bosses of the continental 

 floor appear in many places, entirely surrounded by the 

 deposits of later days. In most of these cases the sur- 

 roimding areas have subsided, leaving the resisting ribs 

 and pillars of the old crust standing firmly. As the tloor 

 of the continent must also have subsided, to allow of the 

 falling in of the upper layers, it is very likely that some 

 contrary upward movement was at the same time given to 

 these bosses and plateaux which now stand above the 

 general level. While subsidence predominated, owing to 

 the contraction of the earth's interior, we may conceive a 

 buckling of the floor, some parts rising as others fell. 

 The sediments slipped into the new hollows from the flanks 

 of the masses across which they once had stretched ; so 

 that a series of dis- 

 locations (faults) —> 



now surrounds the 

 exposed and ele- 

 vated portions of 

 the floor. 



Suess* and 

 Neumayr f have 

 emphasized most 

 strongly the part 

 played by subsi- 

 dence in bringing 

 the resisting knots 

 of the continental 

 floors to light. The 

 word " horst," used 

 by Suess for a ridge 

 left upstanding be- 

 tween two adjacent 

 areas of subsidence, 

 has become extend- 

 ed so as to include 

 any old mass 

 bounded by faults, 

 along which 

 younger strata have 

 slipped down. 

 Favourite examples 

 are found in the 

 Black Forest and 



the Vosges, which are bold highland areas composed mainly 

 of "fundamental" rocks. The Feldberg in the former 

 still rises 4901 feet above the sea, and the Hoheneck 

 near Gerardmer gives us 4580 feet. On the north-east 

 we have to cross the Danube to the Bavarian forest, 

 and on the south-west we must reach the central plateau 

 of France, to find the compeers of these high irregular 

 masses. 



In the uplands of Bohemia we find a wide exposure of 

 the floor of Europe, giving us a strange undulating 

 granite land. Every hollow is set with lakelets, beside 

 which the villages are placed. One may travel day after 

 day across the plateau, at heights of eleven hundred to 

 thirteen hundred feet above the sea. Now one ascends 

 a gentle swelling upland, but the towers of the town 

 in the next hollow can already be descried across the 

 ridge. The descent is thus similarly gentle ; and the 



* " Dcs AntUtz der Erde," Bd. I. (1883), pp. 167, 265, etc. 

 t "ErrgescWchte," Bd. I. (1.886), pp. 309, 327, 331, etc 



1"IG. 2. — Eidge ot Amicut Ku. L.*, .-ecu iron 

 prominence in the landscape. (From a 



broad surface of the ancient rocks is only occasionally 

 broken by a valley. 



The central plateau of France presents very different 

 features. It is far more broken, far more cut into; and 

 portions of it, rising above the general level, are covered 

 with heather, and seem to form independent moorland 

 ranges. But, when we enter fairly on it, we soon recognise 

 the old uniform surface of the plateau, though hundreds 

 of streams have carved deep hollows, into which we descend 

 from time to time. Thus, in the western portion of the 

 plateau, we cross river after river running to the Atlantic, 

 notably the lordly Menne at Limoges, the Briance among 

 the mountains of Pierre-BulHere, the Vc'zi-re at the foot of 

 the steep street of Uzerche, and many other minor streams, 

 until we drop from the rim of these antique highlands into 

 the great valley of the Correze. The roads are carried, 

 however, as far as possible along the ridges between 

 adjacent valleys ; we catch no gUmpse of the streams until 

 we actually cross them, lost as they are in the deep brown 



cuts that they have 

 made ; and looking 

 across country from 

 one high -perched 

 village to another, 

 the upper sturface 

 seems wonderfully 

 level — a plateau 

 undisturbed by 

 structural lines. It 

 is as if we covdd 

 sweep Sutherland 

 clear of the Torri- 

 don sandstone and 

 other stratified 

 masses, the rubbish 

 heaps of the early 

 days of denudation, 

 and reveal the stUl 

 older floor of funda- 

 mental gneiss and 

 •_,'ranite upon which 

 these strata were 

 laid down. 



Upstanding 

 blocks, then, in 

 some places, vast 

 denuded areas in 

 othsrs,reveal tous, 

 across a continent, 

 the nature of the floor on which it lies. The British Isles, 

 as so often happens, serve us as a model of these larger 

 geological features. If the Outer Hebrides recall to us the 

 worn-down surface of North America, from the great lakes to 

 Hudson's Bay, the hills east of Church Stretton (Fig. 2), the 

 JIalvem range, and the little plateau of Charnwood Forest 

 are excellent examples of the " horsts." Formerly these 

 masses were held to be igneous, and later than the rocks 

 through which they now protrude. The patches of old strata 

 upon their flanks were not unnaturally regarded as altered 

 products of the easily recognisable beds on either hand. But 

 more detailed mapping has shown that the floor of Europe 

 is here brought to our notice through the covering of strata 

 that once stretched ttniformly from Wales to the eastern 

 counties.* Old ridges, which were buried even in Cambrian 

 times, have reasserted themselves, their horst-like nature 

 being often evidenced by the great faults that can be traced 



* See, for instance, Geologists' Assopiation, Record of Excursions, 



. 412. - . - 



I i^jnircli Strrttou, Shrop;.liiri',slioHing tliei: 

 photograph by Mr. J. J. Cole, p.h.a.s.J 



