368 



NA TURE 



[February 14, 1895 



Among the gre.it leaders who have passed away within 

 the last twenty-tive years are some who have largely 

 helped to mould the whole fabric of geological science. 

 In the philosophy of geology, when will men cease to 

 venerate the names of Lvell and Darwin.' In laying 

 down the broad lines of stratigraphy, Sedgwick and 

 Murchison, Phillips, Griffith, Logan, Ramsay and Jukes 

 have left behind them imperishable monuments of their 

 genius. In the palxontological domain, among many 

 other illustrious men, Owen, Lonsdale, Salter, Davidson, 

 Morris, Wright and Egerton have left us. In other de- 

 partments of the science, our losses have been likewise 

 heavy — the gentle Scrope, pioneer of volcanic geology ; 

 Robert Chambers, who, after .Agassi/, led the way here in 

 the study of ancient glaciers : David Forbes, who did so 

 much to revive the study of rocks in llritain ; as well as 

 men like Page and .Ansted. who by their popular writings 

 helped to spread abroad an interest in geology. 



Passing from the workers to the work accomplished, 

 we may note a few of the more prominent features 

 in the progress of geology in liritain during the last 

 (|uarter of a century. Space will not permit the 

 survey to be extended to the history of the science 

 on the continent of Europe and in North America. 

 .And first as to the general recognition of the science as 

 an important department of a liberal education. No 

 previous generation has seen so many proofs of this 

 recognition. Many new chairs of (ieology have been 

 founded in our universities and colleges. Te.\t-books, 

 class-books, hand-books, manuals and primers of the 

 science have been issued in edition after edition, and new 

 publications are constantly appearing. Field-clubs, and 

 other local associations, have started abundantly into 

 existence, and field-geology is one of their most attractive 

 features. .\t no time of its comparatively short history 

 has geology been more popular, in the best sense of the 

 word, than it is at the present time. 



If one were asked to specify the feature which above 

 all others has marked the progress of geology in Britain 

 during the last five-and-twenty years, one would reply 

 with little hesitation — the enlarged attention given to the 

 study of rocks, or what is termed the petrographical 

 department of the science. For many years in this 

 countr)- that study was almost entirely neglected. The 

 attractions of fossils and of stratigraphy drove minerals 

 and rocks out of the field. .As David Forbes used sar- 

 castically to complain, geologists had forgotten that 

 their father was a mineralogist. They allowed the 

 petrography of the British Isles to lapse into a condition 

 of dire confusion, without system, without accurate 

 determinations, and without reference to what had been 

 done in the subject abroad. The lirst important step in 

 the way of reform was taken by one who is happily still 

 among us, Mr. H. ('. Sorby. Reviving the method of 

 making thin slices for microscopical examination, de- 

 vised by William Nicol, of Edinburgh, he applied it to 

 the study of rocks, and showed how fruitful it might be 

 made in investigating their history. Though his first 

 paper appeared in 1856, it was long in awakening 

 geologists in this country to the value of the new imple- 

 ment of research thus placed in their hands. It attracted 

 notice sooner in (iermany, and its applicability as 

 demonstrated there, led ultimately to its adoption in the 

 land of its birth. Hut only within the last twenty years 

 has it been acknowledged to be absolutely indispensable 

 in the investigation of the origin and history of rocks. 



The introduction of the microscope as an adjunct in 

 research has entirely revolutionised the study of petro- 

 graphy. .\nd nowhere has the change been so marked 

 as in Britain. The former chaos has been in large 

 measure reduced to order. The rocks of this country, 

 instead of being neglected, are a foremost object of 

 study, and this branch of British geology has been 

 brojght abreast of the petrography of the continent. 



NO. 1320, VOL. 51] 



It is perhaps inevitable that in such a complete trans- 

 formation of methods, the new should be apt to be re- 

 garded as completely replacing the old way. The 

 microscope has done so much, that its potency may not 

 unnaturally be exaggerated, and a tendency so to 

 magnify it may sometimes be observed. But, after all, 

 the great field-relations of the rocks must in the first 

 place claim our attention and guide our reasoning. The 

 minute structures revealed by the microscope may be 

 made admirably serviceable in controlling that reason- 

 ing, and in supplementing the field-evidence by a new- 

 body of data otherwise unattainable. Vet the micro- 

 scope must remain the servant, not the master, in the 

 applications of petrography to the larger questions of geo- 

 logical theory. 



If now w^ turn to the stratigraphical domain of 

 geology, perhaps the first remark that will occur to a 

 rertective observer is that a much closer attention than 

 ever before has been given in Britain to the investigation 

 of the most ancient accessible parts of the earth's crust. 

 The fundamental platform on which the oldest fossil- 

 iferous rocks repose, has been searched for with 

 enthusiasm, and though this enthusiasm has led to 

 mistakes, it has undoubtedly been successful in detect- 

 ing that platform in several places where it was not 

 before supposed to exist. The rocks of the platform 

 have been laboriously investigated, and have been found 

 to include both aqueous and igneous materials. Not 

 only so, but a succession has been observed among 

 them, vast sedimentary masses lying ununiformably on 

 still more ancient gneisses. In these sedimentary accu- 

 mulations no certain trace of organic forms has yet been 

 detected. Nevertheless the search has not been aban- 

 doned. If it should eventually be successful, it would 

 reveal evidence of a fauna or flora older than the oldest 

 relic of life yet discovered in liritain. 



In the region where the most ancient gneisses are 

 typically developed, foliated representatives of almost 

 all the well-known plutonic rocks have been recognised, 

 and perhaps also, though dimly, traces of a group 

 of prima2val sediments, into which igneous masses 

 have made their way. We have thus been able to 

 take several distinct steps backward into the abyss 

 of time. We know more clearly than before the general 

 outlines of two or more great geological periods anterior 

 to the earliest relics of animal life. .\nd as a band of 

 zealous investigators is busy in the exploration of these 

 dim records, it is perhaps not too much to anticipate a 

 rich harvest of discovery from their labours. 



Among the applications of paUcontology to the strati- 

 graphical side of geology, umiuestionably the most 

 important in recent times has been the recognition of 

 life-zones among the stratified formations, and the adop- 

 tion of these as a clue to the interpretation of the 

 sequence of strata, and even of tectonic structure. It 

 is long since the ammonite zones of the Lias, first worked 

 out in Germany, were traced in this country. Subse- 

 quently the pala-ontological platforms in the C halk, so 

 well developed in France, were found to hold good also 

 in England. Still more recently the vertical distribution 

 of graptolites has been shown by Prof. I.apworth to be 

 so restricted that these organisms may be used to mark 

 definite zones in the Silurian system. .\or is it in the 

 animal kingdom only that such restriction has been 

 asserted. The members of an extinct flora have been 

 found to show a more or less marked sequence of genera 

 and species, so that, alike in France and in England, the 

 Carboniferous system has been subdivided into more or 

 less distinct plant-zones. 



The value of this pal.iontological aid in the investi- 

 gation of stratigraphical succession can hardly be over- 

 estimated. Among the undisturbed Secondary rocks of 

 England, indeed, it is not indispensable, for the sequence 

 of then formations and their subdi\i5ion> can be ac- 



