1S53] MEETING OF THE BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 



S3 



Maury, and adopted by the American Government, is, to have 

 the required observations regularly made by the commanders of 

 vessels sent out to sea. I am happy to be able to state to you 

 that our Admiralty have given orders for similar observations 

 to be made by those who have command of English vessels; 

 and we trust also that persons will be appointed without delay 

 for the reduction of the mass of observations which will thus 

 soon bo accumulated. 



The science of Geology may be regarded as comprising two 

 great divisions — the physical and the palseontologieal portions. 

 The former may be subdivided into its chemical and dynamical 

 branches. The chemical department has never made any great 

 progress, though abounding in problems of first rate interest — 

 such for instance, as the formation of coal, the segregation of 

 mineral matter constituting mineral veins of all descriptions, the 

 processes of solidification and crystallization of rocks, of the pro- 

 duction of their jointed and laminated structure, and many others. 

 Interesting experiments are not altogether wanting on points such 

 as these ; "but not sufficient to constitute, as far as I am aware, a 

 positive foundation and decided progress in this branch of the 

 science. The problems, doubtless, involve great difficulties, both 

 as regards the action of the chemical agencies themselves and the 

 varied conditions under which they may have acted. The accom- 

 plished chemist alone can combat the difficulties of the former 

 kind, and the geologist those of the latter. Both these charac- 

 ters must be united in any one who may hope to arrive at the 

 true solution of these problems. We cannot too earnestly invite 

 attention to this branch of geology on the part of those best 

 qualified to contend with its difficulties. 



The dynamical, or more strictly, the mechanical department 

 of the science, has received a much larger share of attention. 

 In fact, almost all theories and speculations of geologists, inde- 

 pendently of organic remains belong to it, and a large portion 

 of the work of geologists in the field has been devoted to the ob- 

 servation of phenomena on which it treats. Phenomena of ele- 

 vation., those which have immediately resulted from the action 

 of the subterranean forces which have so wonderfully scarred and 

 furrowed the face of our globe, have been made the objects of 

 careful research. It is to this probably violent and desolating 

 action that we owe the accessibility of the mineral sources of our 

 mining districts, as well as all those exquisite beauties of external 

 nature which the mountain and the valley present to us. The 

 absence of all order and arrangement would seem on a superfi- 

 cial view, to be the especial characteristic of mountainous dis- 

 tricts; and yet the nice observations of the geologist has detected, 

 in such districts, distinct approximations to general laws in the 

 great dislocations and upheavals in which the mountains and 

 valleys have originated. The more usual law in these phenomena 

 consists in the approximate parallelism of those great lines of dis- 

 location and chains of mountains the formation of which can be 

 traced back to the same geological epoch. That this law is dis- 

 tinctly recognizable throughout districts, sometimes of many 

 hundred miles in extent, is clearly established; but some ge- 

 ologists contend that it may also be recognized as prevailing over 

 much larger geographical areas than any single geological dis- 

 trict presents to us. M. Elie de Beaumont was the originator, 

 and has been the great advocate, of this extension of the theory 

 of parallellism. He extends it, in fact, to the whole surface of 

 the earth : — using the term parallelism in a certain modified 

 sense, to render it applicable to lines drawn on a spherical instead 

 of a plain surface. His theory asserts, that all great lints of dislo- 

 cation, and, therefore, all mountain chains originating in them, 

 wherever situated, may be grouped iuto parallel systems, and 

 that all the lines or mountain chains belonging to any one 

 system were produced simultaneously by one great convulsion 



of the earth's crust. This theory has been advocated by him 

 many years; but he has recently published his latest views res- 

 pecting it, and has made an important addition, which may, in 

 fact, be regarded as an independent theory. Each of the paial- 

 lels already mentioned will have its characteristic direction to 

 which all the lines of that system are parallel. This new theory 

 asserts that these characteristic directions are not determined, 

 as were, by accident or chance, — but that they have certain re- 

 lations to each other, so that the respective systems to which 

 they belong are disposed over the earth's surface according to a 

 distinct symmetrical arrangement. For the details of this curious 

 theory, I can only refer to the author's work, or the analysis 

 which I gave of it last February in my address to the Geological 

 Society. I feel it right, however, to add, that after an attentive 

 examination of the subject, the evidence adduced by M. de Beau- 

 mont in support of the last mentioned theory has failed to convey 

 conviction to my own mind. With reference to the parallelism 

 of contemporaneous lines of elevation, no one, I conceive, will 

 deny the truth of M. de Beaumont's theory in its application to 

 many geological districts of limited extent ; but it will probably 

 be the opinion of most English geologists that, iu attempting 

 to extend it to districts far remote from each other, he has over- 

 stepped the bounds of legitimate induction from facts with which 

 we are present acquainted. Every one, however, who studies M. 

 de Beaumont's work, in whatever degree he may be disposed to 

 adopt or reject the theoretical views of that distinguished geolo 

 gist, will admit the ability and knowledge which he has brought 

 to bear on the subject, and the advantages wdiich must result from 

 the ample discussion which he has given it. 



One favourite subject of speculation in the physical branch of 

 geology has been, at all times since the origin of science, the state 

 of the interior of our planet, and the source of the high tempera- 

 ture observed at all considerable depths beneath its surface. The 

 terrestial temperature at a certain depth in each locality (about 

 80 feet in our own region) remains constant during the whole 

 year, being sensibly unaffected by the changing temperature of 

 the seisons. The same, of course, holds true at greater depths; 

 but the lower we descend the greater is this invariable tempera- 

 ture, the increase being proportional to the depth, and at the 

 rate of 1 Fahr. for about every 60 or 70 feet. Assuming this 

 rate of increase to continue to the depth of 50 miles, we should 

 arrive at a te nperature about twice as great as that necessary to 

 fuse iron, and sufficient, it is supposed, to reduce nearly the 

 whole mass of the earth's solid crust to a state of fusion. 

 Hence the opinion adopted by many geologists is, that our 

 globe does really consist of a solid s ell, not exceeding 40 or 50 

 miles in thickness, and an interior fluid nucleus, maintained in 

 a state of fusion by the existing remains of the heat to which 

 the whole terrestial mass was originally subjected. It might, at 

 first sight, appear that this enormous mass of molten matter, in- 

 closed in so thin a shell, could scarcely be consistent with the gene- 

 ral external condition and temperature of our globe; but it is 

 quite certain that the real external temperature and this supposed 

 internal temperature of the earth are not inconsistent with each 

 other, and that no valid argument of this kind can be urged 

 against the above hypothesis. 



The above estimate, however, of the thickness of the earth's 

 solid crust, entirely neglects the possible effects of the enormous 

 pressure to which the terrestial mass at any considerable depth 

 is subjected. Now, this pressure may produce effects of two 

 kinds, bearing directly on the question before us. In tbe above 

 calculation, terrestrial matter, placed at the depth of 40 or 50 

 miles, with a pressure of more than 200,000 pounds on the 

 square inch, is assumed to be fusible at the same temperature as 

 if it were subjected merely to the ordinary atmospheric pressure; 



