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(tar the lajwe of more than the third part of a century, are only 

 beginning to be duly appreciated, has urged, in hU ' Geology and 

 Volcano* of Central France,' first publuhed in 1826, and in a paper 

 on the excavation of certain valleys, communicated to the Gt 

 S.i-i-'t y a few yean after, the conclusive nature of the evidence of the 

 inmiciue changes in the xurface of the earth which hare been effected 

 by the action of "meteoric agents" that is, of the atmosphere, ii- 

 depositions, and its ever-varying temperature, together with that of 

 the streams they produce, upon the different rocks and materials con- 

 stituting the l.unl, and whieli, in his judgment, entirely supersede the 

 neoewity for referring them to the agency of mighty overwhelming 

 floods and currents, however occasioned. Describing the volcanic 

 formations of the Velay, and in particular the position and actual state 

 of a current of lava, which has spread itself to the width of five, seven, 

 ami nine miles, covering an extensive and elevated table-land formerly 

 called the Coiron, which consists of Jurassic or oolitic strata, he shows 

 that there cannot be the least doubt but that the whole of this lofty 

 tract of secondary strata baa been solely preserved from destruction by 

 its volcanic capping. The remainder of the oolitic formation around, 

 forming the secondary district of the Rhone valley, has been eaten 

 into in .ill directions by various mountain torrents, and gnawed down 

 .ilir.uiic.il to a far lower level. The immense quantity of 

 matter which must have been thus abstracted from the oolitic- mass 

 since the epoch at which this lava was emitted from the now extinct 

 volcano of the Mont Hezen an epoch proved to bo but recent by the 

 fact that, beneath the basalt which it has become, a vegetable soil is 

 found, containing terrestrial shells of a species still existing in the 

 same country " cannot but strike ui with astonishment. There can 

 lie no doubt," Mr. Scrope continues, "that the surface on which the 

 bisalt of the Coiron rests was at that period the lowest of the neigh- 

 bouring levels, or these repeated currents of liquid [flowing] matter 

 c..i Id not have flowed in its direction ; yet at present this same surface 

 vastly overtops evciy ..thu height of the same formation, and ranges 

 upward* of a thousand feet above the average level of the valley-basins 

 of the Ardeche and Rhone on either ride. That a considerable pro- 

 portion of these was excavated by ' ram and rivers," in other words, 

 by meteoric agency such as is still in operation, and not by any diluvial 

 or general flood, is susceptible of direct proof. To attribute, there- 

 fore, the remainder to any other cause of an hypothetical nature 

 unsupported by evidence, would seem to be contrary to the rules of 

 analogy. But the conclusion that the greater portion of the valley of 

 the Rhone has been so recently excavated, and by such agency alone, 

 involves important consequences, since the same agents must have 

 been at work everywhere else, and produced results as stupendous 

 during the same comparatively recent period." (' G. &, V. of Central 

 France,' ch. viii.) In the second edition of this work, published in 

 18o8 (ch. ix., pp. 207-208, note), the author expresses his opinion that 

 r Sir C. Lyell (the most comprehensive advocate for the 

 sufficiency of existing causes) nor the bulk of geologists are " even 

 yet Bufftcientli impressed with the "immense amount of excavation or 

 denudation effected on supra-marine land by the erosive force of the 

 pluvial and fluvial waters." ''That story," he adds, "is yet to be 

 written." 



There are, however, limitations to these changes in the present 

 condition of the earth's surface, some of which are ultimately imposed 

 upon them by their own operation. They were acutely urged by the 

 late Itev. Dr. W. D. Conybeare, a consummate geologist of his time, in 

 his introduction to the ' Outlines of the Geology of England and Wales,' 

 by himself and the late Mr. W. Phillips, and in some papers in the 

 ' Philosophical Magazine' consequent upon the first appearance <>i sir 

 C. LyeU's ' Principles of Geology.' From thirty to forty years have 

 elapsed since the publication of his views, which have been almost 

 forgotten, on which account we cite, from the publication first men- 

 tioned, some of the most apposite : " Over a great part of the earth's 

 surface the influence of these wasting causes is absolutely null, the 

 mantle of greensward that invests it being an effectual protection. 

 The burrows of the aboriginal Britons, after a lapse of certainly little 

 less, and in many instances probably more, than two decades of 

 centuries, retain very generally all the pristine sharpness of their out- 

 line ; nor is the slight fosse that sometimes surrounds them in any 

 degree filled up. Causes, then, which in two thousand years have not 

 affected in any perceptible manner these small tumuli, so often 

 scattered in very exposed situations over the crests of our hills, can 

 have exerted no very great influence on the mass of these hills them- 

 selves in any assignable portion of time which even the imagination of 

 theorist can allow itself to conceive ; and where circumstances are 

 favourable to a greater degree of waste, still there is often a tendency 

 to approach a maximum at which farther waste will be checked : the 

 abrupt cliff will at last become a slojxs, and that slope become defended 

 by it grassy coat of proof. It should appear that even the action of 

 the sea, certainly the moot powerful and important of all those we 

 hire surveyed, has a similar tendency to impose a limit to its own 

 ravages." Dr. Conybeare also considers, in relation to the permanence 

 of the general surface of the globe, the possible effect on the level of 

 the sea of the quantity of materials carric.l int.. it, which he concludes 

 to be absolutely imperceptible a conclusion amply justified by the 

 recent investigation of Mr. A. Tylor, as noticed in the article SEA 

 col. 418. 



The relation of these and other limitations to the consequences of 

 the modern doctrine referring the mighty operations which have 

 formed and modified our continents to causes now in action, acting 

 also under their present conditions, and with only their present forces, 

 has not been adequately considered by subsequent geologists. Dr. 

 Conybeare's views on this subject, we conceive, i" common with tho-e 

 taken by him on other Important points in the philosophy of K' 

 have not received from his successors the consideration they d 

 a circumstance of which the fact of his own withdrawal from the pur- 

 suits of science for many of the later years of his life, may afford 

 gome explanation. 



The subject of the preceding portion of this article is one of ph 

 geography and geology. But we may regard the surface of the globa 

 in a wider philosophical sense, not as confined to that of the land .>mi 

 sea-bed, but as the limit of the extension of the matter constituting 

 our planet ; and therefore, also, of a certain class of the actions whieli 

 maintain it, though not of all the forces to which that matter is 

 subject, some of them extending beyond that limit. In this 

 the earth has two surfaces, that of the land and water taken together, 

 and that of the thin spherical shell of air that rests MJ c 

 encompasses it. The latter is the termination in space of our planet; 

 the former, the termination of the solid and liquid matter of which the' 

 earth, or at least its superficial crust, consists, whatever may l>i: the 

 physical state of the more central interior, of which we know nothing. 

 These surfaces are the final results of the equilibrium which the 

 mutually acting and reacting forces of nature maintain in the globe. 



Thus considered, the subject has an interest of its own, independent 

 of the geographical and geological importance of the surface of the 

 land or solid matter. Though the waters form only a residual film, as 

 it were, of certain materials of the crust which are liquid at the 

 temperature of the surface, a result of the final .equilibrium of the 

 chemical and physical actions taking place below and above, yet their 

 portion of the surface, so much greater than that of the exposed solid 

 matter, or land, has a paramount influence on the constitution of the 

 terminal shell of matter the atmosphere with respect to its a. 

 constituent. The atmosphere, in like manner, is the resultant residue 

 of the physical and chemical actions taking place upon the terraqueous 

 surface, or below, within reach of the atmosphere, but consisting of 

 materials which are aeriform at the mean temperature of the globe ; 

 some, indeed, at all known temperatures ; others within a certain range 

 of them. 



The definite surface of the terraqueous globe, there is reason to 

 conclude, is repeated in that of the atmosphere, the finite extent of 

 which we conceive to be demonstrated by that of the column of 

 mercury or water, or other gravitating fluid in the barometer. It 

 would appear, on first considering the subject, that the only d 

 this surface can undergo will be extensive perpetual undulations of 

 the nature of tides, and disturbances occasioned by the entrance and 

 transit, and perhaps by the ignition, of the bodies which 1 

 meteors. It may, however, be true, agreeably to the views of IVUson, 

 in particular respects anticipated by Graham and by Luke Howard, 

 and with which also harmonise certain inferences regarding the struc- 

 ture of the higher regions of the atmosphere originally drawn by 

 Mr. Brayley, and virtually adopted by the late Professor Daniell that 

 the atmosphere has a terminal film of solid matter frozen air 

 forming upon a subterminal one of liquid matter liquefied air itself 

 passing below into a stratum of air- vapour, and that into a still inferior 

 one of dense air retaining its gaseous condition ; the rarest stratum 

 of the air being thus beneath the summit of the atmospheric column, 

 and not constituting the upper surface, as long tacitly assumed, and as 

 indeed would follow from the law of elasticity of the air considered 

 by itself. In this case, in addition to the movements alluded to, the 

 surface of the atmosphere must b.e in a state of perpetual equilibrated 

 motion and change, the ultimate physical resultant of the continual 

 subversion and restoration of equilibrium, or at least, of the existing 

 tendencies to those conditions, arising from the antagonism of heat 

 and gravitation. 



The complex superficial crust of our planet, of which the surfaces of 

 the atmosphere and of the terraqueous globe are the superior limits, is 

 the final result of the action of the sun upon those surfaces, reacted 

 to by the interior forces of the earth, which the sun, as it were, 

 governs, both by its direct action, gravitative, calorific, light-giving, and 

 magnetic ; and also indirectly, through that of the waters and the air 

 upon the land, the solid, liquid, and aeriform elements of the crust 

 being thus all subject to its action ; while a certain amount of action is 

 also exerted upon them by the radiation of the stars, the suns of other 

 systems. On the surface of the earth, therefore, in its most compre- 

 hensive sense, arc inscribed the indelible and enduring records of all 

 the activities, terrestrial, solar, and celestial, which have produced, and 

 are perpetually reproducing it ; and on that of the terraqueous globe, 

 thus maintained in equilibrium, organic nature and man exist, the 

 well-being of the latter being the end, or final cause, of the whole. 



SURFACES OF THE SECOND DEGREE. This name is given 

 to all those surfaces of which the equation is of the second degree, or 

 can be made a cose of 



<u? + V +* + '2n'y: + 2//'_- r + Zc'xi/ 

 " 



