lU 



KNOWLEDGE. 



[May 1, 1897. 



The " doctrine of descent," so strongly supported and 

 vindicated by Darwin's treatise of 1859, bas found the 

 fullest confirmation in these and other facts of paliPonto- 

 lo^y. The splendid series of remains of fossil horses 

 known to us, illustrating the successive changes in denti- 

 tion and in limb bones, and notably in the digits of the 

 foot, has furnished an example that is dealt with now in 

 every test-hook. (!ope has even argued for the independent 

 origin of the horse, as a species, in America and in Europe, 

 by similar selective influences acting on slightly dissimilar 

 original stocks. 



It must never be forgotten that Darwin himself stands 

 in the first rank of geological observers, whether among 

 raised beaches, or ancient lava-flows, or the coral isles of 

 the Pacific. His diary of bis share in the voyage of 

 H.M.S. Beaijh' appeared as Volume III. of the joint 

 report in 1839 ; but his special geological researches were 

 published in 1812 (coral reefs), 1811 (on volcanic islands), 

 and 1816 (on South America). 



In this last-named year, the newly-formed Geological 

 Survey of Great Britain issued its first volume of memoirs ; 

 the Ordnance Survey of Ireland had published Portlock's 

 "Report on the Geology of Londonderry," etc., three 

 years earlier. De la Beche, Eamsay, and Sir Archibald 

 Geikie — the last-named being equally known as a man of 

 letters — have successively directed the British Survey, 

 Similar surveys were undertaken by most of the European 

 states ; and we owe the fine series of geological maps of 

 the British Isles, the 1 : .80,000 survey of France, the 

 intricate results set down in the Swiss sheets, and such 

 admirable travelling companions as Von Ilauer's map of 

 the Austrian Empire, entirely to the labours of geologists 

 during the last sixty years. Geological mapping is no 

 longer a mere record of the rocks or minerals found at 

 various points on the earth's surface : the relative ages of 

 the strata can now be ascertained by their fossil contents ; 

 and William Smith's original sketch-map of England and 

 Wales, published in 1815, and coloured upon this basis, 

 has, by our time, borne abundant fruit. 



We cannot pass over the striking work of the Geological 

 Survey of India, carried on under difficulties little ex- 

 perienced in Europe ; or the great series of volumes, a 

 monument of public liberality, devoted to geology by the 

 Survey of the United States. Japan and Mexico, among 

 other countries, now furnish their full contribution to the 

 store of geological research. 



Our knowledge of strr.ctural geology has progressed 



with the spread of these 

 accurate surveys, and pri- 

 vate workers have occa- 

 sionally shown how much 

 may be done by patient in- 

 vestigation of a critical 

 district, if aided by that 

 power of comparison and 

 generalization which con- 

 verts the work of a recorder 

 into that of a scientific 

 master. Prof. Lapworth 

 has thus unravelled the 

 complex region of North- 

 West Sutherland, and has 

 shown us, since 1883, how 

 we have in cur highlands 

 the basal sections of truly 

 Alpine mountain chains. Heim in Eastern Switzerland, 

 Baltzer and others in the Central Alps, Bertrand in tJie 

 Juras, Lory in Savoy and in Dauphinr, have revealed 

 the amount of intermingling and overfolding that has gone 



P 



Section of Olivine-basalt from 

 Isle of Mull, as seen under micro- 

 scope, X 2.5. «, Augite ; J), Plagio- 

 claj^tic Felspar; o/. Olivine. 



on in these regions since Oligocene times. The relations 

 of the central granitic and gneissic cores of mountain 

 chains to the strata upon their flanks becomes one of the 

 most interesting questions raised ; and it appears that, far 

 from being the oldest masses, thrust up from below, these 

 cores often represent ro-melted material, which flowed into 

 its present position during the actual period of mountain 

 building. Similarly, I)r. Lawson has shown in C'anada 

 that the " Laurentian " gneiss is intrusive in the Huronian 

 series, and is thus, in part at any rate, by no means the 

 fundamental mass that it was once believed to represent. 



The publication, between 1883 and 1888, of Bas Antlitz 

 der Enle, by Dr. Suess, of Vienna, has exercised a most 

 important influence on students of physical geology. 

 This applies particularly to the relations between the levels 

 of land and water in the past, and between areas of 

 elevation and depression on the earth's surface. The 

 action of old rock-masses in determining the lines of later 

 earth movement has here been emphasized effectively. 



Probably no physical problem has been attacked by 

 geologists more keenly than that of the "Great Ice Age." 

 Since Agassiz, Ramsay, and others pointed out, about 1850, 

 how large a part of the northern hemisphere must have 

 been subject to Arctic conditions of snow and ice, and 

 that these conditions must have prevailed in quite recent 

 geological times, theory after theory has been put forward 

 to account for the widespread phenomena. Prof. -James 

 Geikie published his "Great Ice Age" in 1871 — a work 

 now in its third edition — and may be regarded as the 

 strongest champion of the land- ice theory. Gigantic 

 glaciers, extending even from the Pole, have been invoked 

 by some, while others prefer a combination of land-ice 

 from local centres, with floating ice bringing boulders from 

 a distance. The cold epoch being a certainty. Dr. CroU (a 

 review of whose life appeared in Kno\vlei)(;e for April, 

 1897) set himself to account for it on astronomical 

 grounds ; and his elaborate theory, promulgated in " Climate 

 and Time," in 1875, held sway over the majority of geolo- 

 gists. Quite recently, however, Mr. E. P. Culverwell has 

 reinvestigated the problem on a more modern basis, and 

 regards the astronomical theory as entirely insuflicient ; 

 so we may be thrown back on what were to C'roll, after all, 

 important considerations — the effect of changes in the dis- 

 tribution of anowfields, land, and sea, particularly by 

 causing deviations in currents of warm air and water. 



While geology began its career as a close ally of 

 mineralogy, the excitement of palieontological discovery 

 for a long time caused the rocks themselves to be little 

 studied. The microscopic observations of Cordier ou the 

 constitution of lavas, carried out in lsl5, bore little fruit 

 until 1S5G and 1858, when Dr. Sorby, of Sheffield, drew 

 attention to the value of the microscope in determining 

 the characters and mode of origin of rocks. Ddlesse 

 in France had been a faithful student of polished 

 surfaces ; but Sorby now introduced the general use of 

 sections, or of powdered materials embedded in Canada 

 balsam. The study of minerals in situ by this method 

 became a favourite one in Germany and France, and we 

 owe some of the most important determinative tests to 

 Fouq'ue, Levy, Rosenbusch, and Groth, to mention no other 

 names. The establishment of the first geological labora- 

 tory by Professor Judd in 1877, whereby the teachers 

 trained under the l)epartment of Science and Art, as well 

 as the students of the Royal School of Mines, received 

 practical courses of instruction, probably did more than 

 any other influence to promote the study of rocks in the 

 British Isles and in our colonies. There is little fear now, 

 moreover, of Itritish students becoming adepts in the use 

 of microscopic sections, and forgetful of the true relations 



