THE FARMER'S MAGAZINE. 



307 



subsidiary to true geology, and even to the study of the rocks 

 themBelves. Another point we would remark upon here, as 

 tending to divert popular favour and a due estimation of the 

 merits of this noble science, is the want of a proper and sufli- 

 cient distinction being ordinarily drawn between the specula- 

 tive, theoretical, and practical departments into which this 

 science is certainly divided. Some of its doctrines are moat 

 entirely speculative ; and when any of these are overturned in 

 the popular faith — as assuredly they will be, with the progress 

 of information — they will be so many reverses and drawbacks 

 to its progress. For instance, it is common to hear of the 

 incandescent state of the interior of the globe. This doctrine 

 is purely speculative, but it is not usually set prominently 

 forth as such. It is the more frequently received as one of the 

 established deductions of geology, and we even find writers of 

 eminence placing this speculation in a very decided manner 

 before their readers. It had its origin chiefly iu the fact that 

 in descending into mines, or deep into the earth, an increase 

 of temperature takes place, on the average, equal to one degree 

 of heat for about forty-four feet of depth ; that the shape of 

 the globe itself, that of au oblate spheroid, having its equatorial 

 diameter greater than its polar diameter by about seventy 

 miles, was indicative of an original fluid state ; that on the 

 supposed principle of the condensation of the stellar nebuliE 

 in the heavens, this globe had originally been likewise con- 

 densed from a vaporous condition, by which process great heat 

 had been generated; that granite and other similar rocks exhi- 

 bited the traces of igneous action ; and that from the liuea and 

 evident directions in which volcanic action takes place, it was to 

 be concluded there was an internal sea of molten matter with 

 which they were all connected. The refrigeration of this liquid 

 sphere was supposed to have given rise to a thin consolidated 



[Lion. 1.- Ideal section, illustrative of the primitive structure 

 of the globe, showin? the presumed consolidated crust (*), 

 the central-heated fluid mass («}, and the outer ocean- 

 covering of condensed water (c).] 



crust, which fell in at intervals, and had its fractured portions 

 upturned, as the mass beneath contracted in cooling; that as 

 soon as this film or series of films was sufficiently reduced in 

 temperature to form a protecting crust, the vapour of the 

 atmosphere condensed upon it into seas and oceans, and the 

 deposition of stratified rocks began. The hardened and often 



-^^^^■^rn'^^^l 



LlGN. 2. — Ideal diagram, showing the supposed fracturing 

 of the primitive crust or primeval rock (r), in the progress 

 of solidification by the unequal contraction or expansion 

 of the great central fluid mass.] 



crystalline character of the earliest deposits were thought to be 

 the effect of contact with the heated crust of the globe ; and the 

 elevations of mountain ranges at subsequent epochs, the depres* 



sions and upheavals of lands, and their various associated phe- 

 nomena, were (and even still are by many) imagined to be 

 produced by the continued cooling down of the central portion, 

 and the consequent tilting inwards and upwards of gigantic 

 fragments of the broken and fissured shell. Now very ordinary 

 reflection will soon shew us how purely gratuitous is such a 

 doctrine. That there is an internal heat produced by some 

 cause no one will deny ; that great and wonderful powers have 

 been at work changing the structure of rocks, upheaving, rend- 

 ing, and depressing them, is equally evident ; but in all 

 this there is nothing to prove that the interior of this globe 

 is now in a state of such terrific incandescence, and possess- 

 ing such accumulated intensity of heat as indicated by the 

 calculation of one degree of increase for every forty-four feet 

 of vertical depth. At this rate the boiling point of water 

 would be reached at two miles, the melting point of iron 

 at twenty-four. Now the heat that would melt iron 

 would reduce nearly every known material to the fluid state ; 

 and in the ratio indicated, the intensity at the centre would be 

 equal, as has been calculated, to 450,000 degrees of Fahrenheit. 

 What schoolboy that has cast leaden bullets but knows per- 

 fectly well, no increase of temperature beyond the melting 

 point will take place in the contents of his iron ladle while a 

 single fragment of the solid metal remains. Every one knows 

 too, that if we attempt to melt ice over the fiercest fire, the 

 temperature of the water never rises above freezing point (32°) 

 as long as a single particle of the solid ice remains. Now, as iron 

 melts at about 2,786° Fah., it follows that the temperature of this 

 globe must be reduced to that point at least before any super- 

 ficial consolidation could take place. On the opposite hand, it 

 would also be inferred from the same premises that if the in- 

 candescence had reached the point submitted, the intensity of 

 heat would be sufficient to instantly reduce the thin crust of 

 the globe, and to drive off, with explosive violence, the waters of 

 the oceans and seas. Again, if we placed the end of a bar of iron, 

 or any conducting substance, in a fire, we should find the heat 

 increasing, with a decrease of distance, as we approached the 

 fire ; but in testing the temperature at great depths, it has not 

 been found that the deeper the depth the shorter the distance 

 which produces the additional degree of heat ; on the contrary, 

 it has been found, in some instances, that the periods of space 

 are even more lengthened as we recede from the surface. By 

 this doctrine, too, the granites and crystalline rocks of every 

 region should be all of one age; but it is well known, and may 

 readily be perceived, that they are of very various dates. If 

 we broke through the ice on a pond with a large wedge from 

 beneath, which we allowed to remain between the upturned 

 edges, and if against or upon these elevated portions of ice a 



[LiQN. 3.— Ideal diagram, illustrative of the upheaval of 

 mountains, their geological ages, and the protrusion of 

 their central granitic masses, (a) Vertical section of a pond 

 of water ; {b) crust of ice broken through by a wedge from 

 below, with the disrupted parts elevated on each side ; 

 (c) additional height of water subsequently added ; (rf) new 

 crust of ice.] 



