Nov. i6, 1871J 



NA TURE 



53 



melted state, they would now have been seen in the condition of 

 glass or slag, and not with the granular or crystalline texture 

 which they actunlly possess. Hall demolished this objection by 

 melting basalt into a glass, and then by slow cooling reconvcrb 

 ing it iii'o a granular substance like the original rock. Ilutton 

 had maintained that under enormous pressure, such as he con- 

 ceived must e.xist under the ocean, or deep within the crust of 

 the earth, even limestone itself might be melted without losing 

 its carbonic acid. This was ridiculed by his opponents, on 

 wlioni he retorted that they "judged of the great 0]3erations of 

 the mineral kingdom from having kindled a fire and looked into 

 the bottom of a little crucible.'' Hall, however, to whom fire 

 and crucible were congenial implements, resolved to put 

 the q\iestion to the test of experiment, and though, out of 

 ileference to his master, he delayed his task until after the 

 death of the latter, he did at last succeed in converting lime- 

 stone, under various great pressures, into a kind of marble, and 

 even in reducing it to complete fusion, in which state it acted 

 powerfully on other rocks. He concluded his elaborate essay 

 on this subject with these words, " This single result affords, I 

 conceive, a strong presumption in favour of the solution which 

 Dr. Hutton has advanced of all the geological phenomena; for 

 the truth of the most doubtful principle which he has assumed 

 has thus been established by direct experiment." 



Though they saw clearly the proofs which the rocks afford us 

 of former revolutions, neither Hutton nor his friends had any 

 conception of the existence of the great series of fossiliferous 

 formations which has since been unfolded by the labours of later 

 observers — that voluminous record in which the history of life 

 upon this planet has been preserved. They spoke of " Alpine 

 schistus," "primary " or " secondary " strata, as if the geological 

 past had consisted but of two great ages — the second replete 

 with traces of the destruction of the first. " The ruins of an 

 older world," said Hutton, "are visible in the present structure 

 of our planet." He knew nothing of the long, but then undis- 

 covered, succession of such "ruins," each marking a wide in- 

 terval of time. Nevertheless, for the establishment of the great 

 truths which Hutton laboured to confirm, such knowledge was 

 not necessary. On the other hand, it was most needful tliat the 

 significance of that discordance between the older and newer 

 strata which Hutton recognised should be persistently proclaimed. 

 And the Huttonians, in spite of their limited range of know- 

 ledge and opportunity, saw its value and held by it. 



2. But it was not merely, or even chiefly, for their exposition 

 of the structure and history of the rocks under our feet that the 

 geologists of the Scottish School deserve to be held in lasting 

 remembrance. They could not, indeed, have advanced as far 

 as they did in expounding former and ancient conditions of the 

 planet, had they not, with singular clearness, perceived the order 

 and system of change which is in progress over the surface of the 

 globe at the present day. It was their teaching which first led 

 men to see the harmony and co-operation of the forces of nature 

 Avliich work within the earth, with those which are seen and felt 

 upon its surface. Hutton first caught the meaning of that con- 

 stant circulation of water which, by means of evaporation, winds, 

 clouds, rain, snow, brooks, and livers, is kept up between land 

 and sea. He saw that the surface of the dry land is everywhere 

 being wasted and worn away. The scaqied cliff, the rugged glen, 

 the lowland valley, are each undergoing this process of destruc- 

 tion ; wherever land rises above ocean, there, from mountain- 

 top to sea-shore, degradation is continually going on. Here and 

 there, indeed, the dibris of the hills may be spread out upon 

 the plains ; here and there, too, dark angular peaks and crags 

 rise as they rose centuries ago, and seem to defy the elements. 

 But these are only apparent and not r^-al exceptions to the uni- 

 versal law, that so long as a surface of land is exposed to the at- 

 mosphere it must suffer degradation and removal. 



But Hutton saw, further, that this waste is not equally distri- 

 buted over the whole face of the dry land, that while, owing to 

 the greater or less resistance offered by different kinds of rocks, 

 the rate of decay must vary indefinitely, the amount of material 

 must necessarily be greatest where the surplus water flows off 

 towards the sea, that is, along the channels of the streams. 

 Water-courses, he argued, are precisely in the lines which water 

 would naturally follow in running down the slope of the land from 

 its water-shed to the sea, and which, when once selected by the 

 surplus drainage, would necessarily be continually widened and 

 deepened by the excavating power of the rivers. Hence he re- 

 garded the streams and rivers of a country as following the lines 

 which they had chiselled for themselves out of the solid land, and 

 hus he aitived at the deduction that valleys have been, inch by 



inch and foot by foot, dug out of the solid framework of the land 

 by the same natural agents — rain, frost, springs, rivers — by which 

 they are still made wider and deeper. " The mountains," he 

 said, "have been formed by the hollowing out of the valleys, 

 and the valleys have been hollowed out by the attrition of 

 hard materials coming from the mountains." This is a doctrine 

 which is only now beginning to be adequately realised. Yet 

 to Hutton it was so obvious as to convince him, to use his 

 own memorable words, " that the great system upon the surface 

 of this earth is that of valleys and rivers, and that however this 

 system shall be interrupted and occasionally destroyed, it would 

 necessarily be again formed in time while the earth continued 

 above the level of the sea." 



Although these views were 'again and again proclaimed by 

 Hutton in the pages of his treatise, and though Playfair, catching 

 up the spirit of his master, preached them with a force and elo- 

 quence which might almost have insured the triumph of any cause, 

 they met with but scant acceptance. The men were before their 

 time ; and thus, while the world gradually acknowledged the 

 teaching of the .Scottish school as to the past history of the rocks, 

 it lent an incredulous ear to tliat teaching when dealing with the 

 present surface of the earth. Even some of the Huttonians 

 tliemselves refused to follow their master when he sought to ex- 

 plain the existing inequalities of the land by the working of the 

 same quiet unobtrusive forces which are still plying their daily 

 tasks around us. But no incredulity or neglect can destroy the 

 innate vitality of truth. And so now, after the lapse of fully two 

 generations, the views of Hutton have in recent years been re- 

 vived, and have become the war-cry of a yearly increasing 

 crowd of earnest hard-working geologists. 



While they insisted upon the manifest proofs of constant and 

 universal decay over the surface of the globe, the Scottish geolo- 

 gists no less strongly contended that the decay «'as a necessary 

 part of the present economy of Nature, that it had been in pro- 

 gress from the earliest periods in the history of the earth, and 

 that it was essential for the presence of organised beings upon the 

 planet. They pointed to the vegetable soil, derived from the 

 decomposition of the rocks which it covers, and necessary for the 

 support of vegetable life. They appealed to the vast quantity of 

 sedimentary rocks forming the visible part of the crust of the 

 earth, and bearing witness in every bed and layer to the degrada- 

 tion and removal of former continents. They showed that the 

 accumulated ddbris of the land, carried to sea, was there spread 

 out on the sea-floor to form new strata, which, in due time 

 hardened into solid rock, would hereafter be upheaved to form 

 the framework of new lands. 



Such was the geology of the .Scottish School. It w'as based 

 not on mere speculation, but on facts drawn from mountain and 

 valley, hill and plain, and tested as far as was then possible by 

 the scrutiny of actual experiment. It strove, for the first time in 

 the history of science, to evolve a system out of the manifold 

 complications of nature, to harmonise what had seemed but the 

 wild random working of subterranean forces with the quiet 

 operations in progress upon the surface of the earth, to under- 

 stand what is the present system of the world, and through that 

 to peer into the history of the earlier conditions of the planet. It 

 taught that the earthquake and volcano were parts of the orderly 

 arrangement by which new continents were from time to time 

 raised up to supply the place of others which had been worn 

 away ; that the surface of the land required to decay to furnish 

 life to plants and animals ; that in the removal of the debris thus 

 produced mountains and valleys were carved out ; and that in the 

 depths of the ocean there were at the same time laid down the 

 materials for the formation of other lands, which in after ages 

 would be upheaved by underground forces, to be anew worn 

 away as before. The Scottish School proclaimed that in the in- 

 organic world there is ceaseless change, that this change is the 

 central idea of the system, and that in its constant progress lie 

 the conditions necessary for the continuance of our earth as a 

 habitable globe. 



That Hutton and his followers should have seen only a part 

 of the truth, that they did not perceive the full scope which 

 their views would ultimately acquire, that they fell into errors, 

 and attached to some secondary parts of their system an im- 

 portance which we now see to have been misplaced, is only 

 what may be said of any body ot men who, at any time, 

 have led the way in a new development of human inquiry. 

 But, after all allowance is made for such shortcomings, we see 

 that their errors were for the most part on mere matters of 

 detail, and that' he fundamental principles which they laboured 

 to establish have become the very life and soul of modern geology 



