GENERAL INDICATIONS. 787 



may reasonably impute to internal heat the high temperature of the climate of far remote 

 ages, reduced to its present statical condition in the refrigeration of the surface by 

 radiation. Whatever be the true theory of volcanic action, whether the mechanical of 

 Cordier, or the chemical of Daubeny, or both combined, each involves the existence of 

 heated fluid masses in the earth which the phenomena display, while thermal springs 

 occurring in regions far apart from any modern volcanoes, and the raising of the 

 temperature as we descend below the surface, point to a generally heated interior, if not 

 to an " ocean of- molten rock," not far below the external shell. 



It may be justly inferred also, that those causes which in former ages operated to 

 modify the aspect of the earth, and those that are now in action, are identical in their 

 nature atmospheric, aqueous, and igneous agencies. But this conclusion leaves it an 

 open question, whether their intensity was not much greater in ancient than in modern 

 eras. Mr. Lyell has answered here in the negative, contending that the causes of 

 geological change now acting upon the globe, and with no more energy than at present, 

 are amply sufficient to explain the revolutions which the crust of the earth has undergone, 

 all its fractures, elevations, and subsidences. No catastrophes are admitted into his creed 

 greater than what now take place, and all effects which transcend any single effect of 

 existing causes are resolved into the result of an agency repeating its play through an 

 indefinite series. Still, though an authority so eminent demands all respect, there are 

 various considerations which favour the hypothesis, that while the geological processes of 

 the current epoch are in all cases the antitypes of those which operated in remote eras, 

 they are less intense than formerly. Thus vertical movements of the strata gradually 

 transpiring to the amount of a few feet in a century, or suddenly occurring through 

 paroxysmal excitement, are among the events of the present era ; but if the elevatory force 

 has exerted its maximum energy during the historic period, it is difficult to conceive of a 

 succession of such movements uplifting vast chains of mountains and continents, several 

 thousand feet, as we know to have taken place in early times. It may also be observed, 

 that in passing through the series of secondary rocks, we have noticed sudden and 

 remarkable changes in the organic remains of successive systems of strata, which seem to 

 intimate a long period of repose, followed by destructive catastrophes, and succeeded by 

 restored tranquillity ; for the supposition that races of plants and animals became gradually 

 extinct during periods of repose, new species gradually replacing them by a law of nature, 

 is not sustained by the facts that are common to modern times. Though we have an 

 example of the extinction of a species, as in the case of the dodo, and perhaps the Apteryx 

 australis of New Zealand, no instance of the creation of a new species has been discovered 

 during the history of the human race. Nor have we any specimen of the more important 

 of the older rocks, stratified and unstratified, mica-schist, gneiss, granite, and syenite, 

 having been produced during the present cycle of geological change. Granitic varieties 

 indeed may still be elaborating in the bowels of the earth, where the deep volcanoes strike 

 their roots, but their abundant obtrusion at the surface in by -gone ages at least proves a 

 fiery activity operating then upon the superficies more powerful than the igneous agencies 

 now brought to bear upon it. Upon the whole, the conclusion is most probable that 

 while instruments of change have been incessantly modifying and altering the condition 

 of our globe, their intensity has varied, and was far greater in ancient than in modern 

 times, though the causalities themselves, mediate as well as primary, have been of the 

 same kind. 



But decisively is the sublime truth unfolded by' geological examinations, that the 

 present terrestrial constitution is not a chance condition ; that its memorials of decay and 

 change, which everywhere present themselves, are not instances of defective arrangement, 

 as the untutored mind is apt to conceive; that its very instability is an essential 



3E 2 



