9S9 



GEOLOGY. 



GEOLOGY. 



090 



date, to 8675 feet : while in the Harz the older mountains (Brocken) 

 rise to 3739 feet; in Wales (Snowdon) to 3675 feet; in the Grampians 

 (Ben Nevis) to 4350 feet. The highest point of Norway (Schnee- 

 Huten) is more than 8000 feet above the sea, but there can be no 

 doubt that violent as well aa gradual upward movements affected the 

 Scandinavian ridges to a late geological era. 



liaised in this manner by violent or gradual movements out of the 

 sea, the dry land has since been subjected to waste by atmospheric 

 action ; and there is no doubt of the truth, that to different sorts of 

 rock belong some differences of aspect, some characteristic scenery. 

 The forms of the hilla and valleys are not the same in the gneiss and 

 mica-schist of the Grampians ; the clay-slate ranges of Wales ; the 

 limestone of Derbyshire ; the oolites of Gloucestershire ; the chalk of 

 Wiltshire ; even single rocks and waterfalls have distinctive charac- 

 ters, and the whole aspect of a country changes with its geological 

 structure. It thus appears that the nature and structure of the rocks, 

 their elevation above the sea, and the manner in which they attained 

 it, and the intensity and duration of the atmospheric agencies which 

 have since affected them, are the elements which determine in every 

 instance the physical aspect of a country. 



No question in geological theory has been the subject of so much 

 debate, with so little of correct reasoning, as that of the origin of 

 valleys. By Dr. Hutton it was contended that atmospheric agency 

 and running waters had excavated valleys ; by De Luc the subsidence 

 of the crust of the earth was invoked ; Omalius D'Halloy introduced 

 the consideration of dislocations on the line of the valley ; and Dr. 

 Buckland appealed to the overwhelming force of a general flood. 

 None of these views is entirely wrong ; each contains partial truth ; 

 and the complicated problem of the inequalities of the surface of the 

 earth can be solved by combining them. 



By violent elevation from the sea, rocks of whatever nature or 

 structure, must have been variously broken and fissured. It is con- 

 ceivable that some of these fissures might descend below the level of 

 the water. During the elevation some considerable effect on the 

 forms of the ridges and hollows would be produced by the agitated 

 water, but the smaller modifications which they have experienced 

 must bo ascribed to atmospheric agency. In these few words we have 

 the history of the rough hills, abrupt vallays, and deep lakes which 

 belong to mountain chains like the Grampians, Alps, and Pyrenees. 



By gradual risings or interrupted lifts of the bed of the sea, other 

 phenomena would arise ; the action of the sea upon the rocks, succes- 

 sively brought within the sphere of its littoral movements, would 

 concur with the form of pre-existing land, and the entrance of its 

 drainage waters, in extending the old and producing new valleys. 



In the next diagram (jig. 6) the same country is represented as 

 rising out of the sea, which penetrates by the transverse valley across 

 the ridges of rocky hills, and flows round them up the vales of clay ; 

 its waves wasting the clays under the cliffs, and causing the top to 

 fall, exactly on the same principle that waterfalls at this day, by 

 wasting the argillaceous basis, break down the crowning limestone beds 

 throughout all the north of England. 



The Giesbach, on the lake of Brienz, compared with the Staub- 

 bach ; Hardrow Force in Yorkshire, or Ashgill Force iu Cumberland, 



; contrasted with the Fall of Lodore, near Keswick, are iu this respect 

 very instructive ; nor should the cases be neglected where, as oil the 



1 coast near Scarborough, Robiuhood's Bay, aud Whitby, the sea now 

 flows among the lias and oolitic rocks, and wastes their argillaceous 

 parts on a small scale, almost exactly as in the above explauatiou it 



I is supposed to have wasted the similar but thicker clays, when the 



1 whole system was rising above the waves. Pleasing illustrations of 

 this kind of action occur in the Medlock at Manchester, the Greta 



j near Ingleton, the sea-coast near Heysham, Sunderlaud, Berwick, &c. 

 In the Isle of Wight the fresh-water limestones and clays, and the 

 various beds of the plastic clay series about Culver, offer abundance 

 of curious examples. 



The same mode of action is traced in the forms of mountains and 



hills which are composed of strata of unequal resisting power ; as 



mountain limestone and shale in the Yorkshire dales, oolite and 



clay in the Gloucestershire Hills, Normandy, or the Jura mountains. 



The diagram (fig. 7), given below, represents a cross-section of Weasley 



; Dale, which for a great part of its length exhibits, wherever a consi- 

 derable rock of limestone comes to the surface, a decided projection 

 and terrace on the hill side, aud below every such rock a slope formed 

 hi the alternating shales and thin sandstones. 



How much of this appearance is due to atmospheric action and 

 rain since the river Yore has been running in its present bed, aud 

 how much to the influence of water bathing the hill-breasts at higher 

 levels, is not easy to determine ; but the correspodence of the strata 

 on the opposite sides is such as to leave no doubt that all the vast 

 space of the valley has been really excavated out of continuous 

 strata; and the survey of the whole line of this and other rivers 

 appears to refute the opinion that the existing drainage waters have 

 carried off much of the detritus. 



To conclude this brief notice of the origin of the principal inequali- 

 ties on the earth's surface, it may be proper to remark that the view 

 here given of the excavation of valleys at the time of the rising of 

 rocks from the sea, explains the otherwise unintelligible phenomenon 



. of dry valleys in chalk, oolite, and other calcareous strata, which 



Valley of the Yore, near Hawes. 



The greater number of these extended or new valleys would be 

 directed at right angles to the axis of elevation in progress, and there- 

 fore, on the dry land, the greater number of valleys originating in these 

 circumstances will be found to run with the dip of the strata. How 

 exactly this agrees with the general character of the drainage channels 

 of the secondary strata of England above the red-sandstone requires 

 only to be mentioned ; and it has been already shown that in all the 

 south-eastern part* of England where these strata occur there is sum- j 

 cient evidence that the elevation of these rocks was due to gradual 

 and long-continued, not violent and transitory movements. While 

 snaii gradual movements occurred, and strata of unequal hardness 

 and different structure (as limestone and clay, or sandstone, in diagram, j 

 fly. 4), were brought within the range of littoral action, these would 

 be unequally affected by the tidal and other currents ; the softer parts 

 would be worn away, the harder remain ; and thus the red marl j 

 would be wasted parallel to the coast-line, or to a certain depth in 

 the water, below the cap of lias limestone ; the lias clays would yield 

 beneath the crown of lower oolite ; the Oxford clay be excavated 

 below the middle oolite ; and the Kimmeridge clay form a vale 

 between the middle and upper oolites. 



The exact conformity of this with the appearance in nature is well 

 known. The general character of the actual drainage, as Dr. Smith 

 hag often and elegantly explained, may be represented in diagram, 

 ji'j, 5, where lit and mm m are valleys descending on the slopes of 

 the strata, N N and P, valleys formed iu softer strata parallel to the 

 coast ; T a transverse valley uniting the others. 



wind and unite like the branches of a river, and have slopes and 

 features such as to prove their origin from moving water, but contain 

 no trace of a stream, no mark of a spring, and often no alluvial 

 sediment. 



It appears also necessary to remark that, independent of the facts 

 here stated, there must be some importance attached to the effects 

 likely to be produced by the violent agencies, whatever they were, to 

 which the origin of diluvial phenomena is ascribed. The essential 

 thing however in this case being a relative change of level of land and 

 sea, the result of the watery agitation could only be to modify in a 

 greater or less degree the more considerable effects of previous 

 agencies of longer duration. Gravel heaped in particular places 

 conceals some of the earlier slopes of land, and covers with irregular 

 hillocks nn original sea-plain, but the great features of the country 

 remain comparatively unaffected by these transient disturbances. 



Life on the Globe. Geology enables us to behold, in the present 

 varied and complicated arrangement of land and water, the result of 

 many and repeated actions of causes which are not yet extinct, but 

 continually occupied in similar operations, in different situations, and 

 under different circumstances. The laud which has been raised from 

 the sea by internal expansion seems to be slowly wasted away by the 

 action of water, and again restored to the deep. But new land is 

 formed by these ruins, and volcanic fires are yet competent to raise or 

 depress the bed of the sea. 



The land is not all of the same antiquity; some regions must have 

 been covered by trees, perhaps or rather certainly traversed by quad- 



