54 



MEETING OF THE BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 



[1853 



whereas the temperature of the fusion may possibly be very 

 muck increased i y such immense pressure as that which I have 

 mentioned. In such case, the terrestrial matter may be retained 

 in a solid state at much greater depths than it otherwise would 

 be: — i. e., the solid crust may be much thicker than the above 

 estimate of 40 or 50 miles. Again, in this estimate, it is as- 

 sumed that heat will pass as easily through the most superficial 

 portion of the earth's mass as through the compressed portions 

 at considerable depths. Now in this assumption, there is, I 

 think, a great a priori improbability, and especially with refer- 

 ence to those superficial rocks in which observations on the 

 increase of terrestrial temperature in descending have generally 

 been made, for these rocks are, for the must pait, sedimentary 

 strata, which are in general, independently of the effect of pressure, 

 doubtless, worse conductors than the older, more compact, and 

 more crystalline rocks. But if heat passes through the lower 

 portions of this terrestial mass with more rapidity than through 

 its uppermost portion — i e., if the conductive power be greater 

 at greater depths — the temperature at considerable depths must 

 increase more slowly as we descend than it is observed to in- 

 crease at the smaller depths to which we can penetrate, — and 

 consequently it would be necessary in such case, to descend to a 

 greater depth before we should reach the temperature necessary 

 to produce fusion. On this account also, as well as from the 

 increased temperature of fusion, the thickness of the earth's crust 

 may be much greater than the previous estimate would make it. 

 It has been for the purpose of ascertaining the effects of great 

 pressure that Mr. Fairbairn, Mr. Joule, and myself, have under- 

 taken the experiments in which we have for some time been 

 engaged at Manchester. The first object in these experiments is, 

 the determination of the effect of pressure on the temperature of 

 fusion of as many substances as we may be enabled to experiment 

 upon. We expected to meet with many difficulties in the use of 

 the enormous pressures which we contemplated, and these ex- 

 pectations have certainly been fully verified ; but we were also 

 satisfied that those difficulties might be overcome by perseverance 

 and patience, and in this also we have not been disappointed— 

 for I may now venture to assert that our ultimate success, with 

 respect to a number of substances, is beyond doubt. Without 

 the engineering resources, however, at Mr. Fairbairn's command, 

 success would have been hopeless. 



At present our experiments have been restricted to a few sub- 

 stances, and those of easy fusibility ; but 1 believe our apparatus 

 to be now so complete for a considerable range of temperature, 

 that we shall have no difficulty in obtaining further results. 

 Those already obtained indicate an increase in the temperature 

 of fusion proportional to the pressure to which the fused mass 

 is subjected. In employing a pressure of about 13,000 lbs. to 

 the square inch on bleached wax, the increase in the temperature 

 of fusion was not less than 30 ° Falir., — about one-fifth of the 

 whole temperature at which it melts under the pressure of the 

 atmosphere. We have not yet ascertained the degree in which 

 the conductive power of any substance may be increased when 

 solidified under great pressure. This point we hope to investi- 

 gate with due care ; and also to determine the effects on sub- 

 stances thus solidified, with respect to their density, strength, 

 crystalline forms, and general molecular structure. We thus hope 

 to obtain results of general interest and value, as well as those 

 which may bear more directly on the questions which first sug- 

 gested the experiments. 



Among researches for determining the nature of the earth's 

 crust at greater depths than those to which we can penetrate, I 

 must not omit to mention Mr Mallet's very elaborate report on 

 Eart quakes, contained in the last two volumes of the Reports of 

 the Association. This Earthquake Catalogue is preceded by 



an account of some very interesting and carefully conducted ex- 

 periments on the transmission of vibrations through solid ni-dia. 

 These results will be found of great value, whenever the subject 

 of earthquakes shall receive that careful attention which it so well 

 deserves. Insulated observations, and those casual observations, 

 and those casual notices which are now frequently given of 

 earthquake phenomena, are utterly useless for scientific purposes. 

 There are no observations which require more to be regul; ted by 

 system and combination than those of the phenomena in ques- 

 tion ; and I should rejoice to see the influence of the association 

 exerted for this purpose when some efficient mode of proceeding 

 shall have been devised. 



Some of the most interesting of recent discoveries in organic 

 remains are those which prove the existence of reptilian life 

 during the deposition of some of our oldest fossiliferous strata. 

 An almost perfect skeleton of a reptile belonging to the 

 Batrachians or Lacertians was lately found in tlie Old Red 

 Sandstone of Morayshire. The remains of a reptile were filso 

 discovered last year by Sir Charles Lyell and Mr. Dawson in 

 the coal measures of Nova Scotia; and a batrachoid fossil lias 

 also been recognized in British coal shale. But the most curious 

 evidence of the early existence of animals above the lower orders 

 of organization on the face of our globe, is that afforded by the 

 footprints discovered a short time ago in Canada by Mr. Logan 

 on large slabs of the oldest fossiliferous rocks, — those of the Silu- 

 rian epoch. It was inferred from the more imperfect specimens 

 first brought over, that these footmarks were the marks of some 

 reptile ; but more perfect examples, afterwards supplied by Mr. 

 Logan, satisfied Prof. Owen that they were the impressions of 

 some animal belonging to the Articulata, probably a crustacean. 

 Thus the existence of animals of the reptile type of organization 

 during the carboniferous and Devonian periods is clearly estab- 

 lished ; but no evidence has yet been obtained of the existence of 

 those animals during the Silurian period. After the discoveries 

 which I have mentioned, however, few geologists will perhaps be 

 surprised should we hereafter find that higher forms of animal 

 life were introduced upon the earth dining this early period than 

 have yet been detected in its sedimentary beds. 



Many of you will be aware that there are two theories in 

 geology , which may be styled the theories of progression and of 

 non-progression respectively. The former asserts that the mat- 

 ter which constitutes the earth has passed through continuous 

 and progressive changes from the earliest state in which it existed 

 to its actual condition at the present time. The earliest state 

 here contemplated may have been a fluid, or even a gaseous state, 

 due to the enormous primitive heat of the mass, and it is to the 

 gradual loss of that heat that the progressive change recognized 

 by this theory is chiefly attributed. The theory of non-progres- 

 sion, on the contrary, recognizes no primitive state of our planet 

 differing essentially from its existing state. The only changes 

 which it does recognize being those which are strictly periodical, 

 and therefore produce no permanent alteration in the state of our 

 globe. With reference to organic remains, the difference between 

 these theories is exactly analogous to that now stated with re- 

 ference to inorganic matter. The theory of progression asserts 

 that there has been a general advance in the forms of organic 

 life from the earliest to the more recent geological periods. This 

 advance must not be confounded, it should be observed, with that 

 progressive developement according to which animals of a higher 

 organic structure are but the improved lineal descendants of those 

 of the lowest grade, thus abolishing all distinction of species. It 

 is merely meant to assert that the higher types of organic being 

 are far more generally diffused at the present time, and far more 

 numerous and varied than they were at the earlier geological 

 periods; and that, moreover, at the earliest of those periods which 



