244 



NATURE 



[July [5, 1897 



lavas of the plateaux which are more or less meta- 

 morphosed around them, and are traversed by a fringe 

 of finer-grained sills and veins of dolerite, gabbro, trocto- 

 lite, picrite, &c., vi'hich have often insinuated them- 

 selves between the sheets of the plateau-basalts. The 

 coarse-grained and banded gabbros may have con- 

 solidated at some depth ; at least nothing is yet certainly 

 known of their superficial equivalents. 



The third stage of activity, probably long posterior to 

 the second, likewise furnishes no evidence of any super- 

 ficial ejection. It is recorded by a series of markedly 

 acid rocks — obsidians, felsites, rhyolites, porphyries, 

 granophyres, and granites. These rocks form huge 

 conical hills, which in outward aspect recall the trachytic 

 Puys of Auvergne. They traverse alike the plateau- 

 basalts and the bosses of gabbro, into which they send 

 many dykes and veins. They also project numerous 

 thick sills into the formations lying underneath. The 

 rocks around these acid protrusions have been greatly 

 metamorphosed, while the granophyres and granites 

 have in turn undergone considerable change in com- 

 position from having caught up and assimilated some- 

 times a fourth of their bulk of basalt or gabbro. 



After the uprise of the granophyres with their sur- 

 rounding network of felsitic dykes and veins, a new 

 ascent of basic material manifested itself, recalling that 

 of the earliest basalt-dykes, but on a minor scale. The 

 dykes then formed cut all the other members of the vol- 

 canic series, including the granophyres. No trace remains 

 of any superficial discharges connected with these latest 

 dykes. If they ever gave rise to outflows of lava, these 

 have long since disappeared in the vast denudation 

 which the Tertiary volcanic rocks have undergone. 



The latest eruptions of North-Western Europe, forming 

 the Tertiary volcanic series, are shown by Sir Archibald 

 Geikie to have far exceeded in area, and possibly also in 

 bulk of material discharged, all the eruptions that had 

 preceded them in the geological record. 



We learn further that neither in their forms or products, 

 nor by their extent and vigour, did the volcanic mani- 

 festations of the successive ages of the geological past 

 materially differ from those of the present time. There 

 is assuredly no evidence that volcanic energy has 

 gradually waned since the dawn of geological history. 



A consideration of the distribution of the volcanic 

 rocks in time shows not only how singularly uniform the 

 course of volcanic activity has been, but that there is no 

 evidence of the cessation of any of the broader petro- 

 graphical types during geological history. Quite as 

 much variety may be observed among the erupted 

 materials of Tertiary time in Britain as among those of 

 the early ages, when the earth was younger and its vol- 

 canic vigour might be supposed to have been greater 

 and more varied than it is now. 



From the evidence detailed in these volumes, it appears 

 that the sequence from basic to acid discharges was on 

 the whole characteristic of each eruptive period. It is 

 obvious however, the author observes, that as the pro- 

 trusions of successive periods took place within the 

 same limited geographical area, the internal magma 

 during the interval between two such periods must in 

 some way have been renewed as regards its constitution, 

 for when, after long quiescence, eruptions began once 

 NO. 1446, VOL. 56] 



more, basic lavas appeared first, and were eventually 

 followed by acid kinds. 



Various opinions have been propounded as to the 

 cause or causes of the differentiation observable in 

 erupted masses, but none of them are entirely satisfac- 

 tory. We must await the results of further exploration 

 in the field and of continued research in the laboratory. 



What appears to have taken place within a subter- 

 ranean molten magma which has been propelled into the 

 earth's crust as a boss or laccolite, with or without a 

 connected system of dykes, may possibly be made to 

 throw some light on the remarkable changes in the 

 characters of lavas successively erupted from the same 

 vent during the continuance of a volcanic cycle. Whether 

 or not any such process of differentiation can be proved 

 to take place within a subterranean volcanic reservoir, 

 the sequence of erupted lavas bears a curious resem- 

 blance to the order in which the constituents of some 

 large bosses succeed each other frorri margin to centre 

 (vol. i. p. 92). 



Sir Archibald Geikie has written the history of the 

 ancient volcanoes of Britain in a series of attractive 

 chapters, which he has illustrated with more than four 

 hundred sketches, photographs and maps. But the fine 

 work with which he has enriched science is much more 

 than a detailed description of the crystalline rocks of his 

 own country. He elucidates their structure and arrange- 

 ment, and explains thereby their history. He rises from 

 a consideration of facts to a discussion of the cause of 

 volcanic phenomena. He makes the extinct volcanoes 

 bear their testimony in favour of the uniformity and 

 unity of the laws of nature. His work will remain one 

 of the monuments of our time, establishing for the 

 future the conception of the continuity of volcanic 

 phenomena from the earliest periods, and, so far as the 

 geological records go, demonstrating that the interior of 

 our planet has reacted on its exterior in the same way 

 and with the same results. Chas. Barrois. 



AMERICAN MATHEMATICS. 

 Higher Mathematics : a Text-book for Classical and 

 Engineering Colleges. Edited by Mansfield Merriman 

 and Robert S. Woodward. Pp. xi -I- 576. (New 

 York : John Wiley and Sons. London : Chapman 

 and Hall, Ltd., 1896.) 



THIS is a style of mathematical treatise to which we 

 are not accustomed in this country, from the luxury 

 of the print and size of page, as well as for the refreshing 

 novelty and interest of the contents. 



Till recently, it was thought that the study of mathe- 

 matics was not likely to flourish in America, as trop 

 vieux jeu by the side of the new physical and biological 

 sciences. To-day, however, it is the American student 

 who is the most enthusiastic follower of recent mathe- 

 matical development, while we in this country are being 

 left far behind. 



The words on the title-page— A Text-book for Classical 

 and Engineering Colleges— the equivalent of our own— 

 For Schools and Colleges — is not, however, taken, as 

 with us, to be the rendering of In usum Delphini j all 

 human interest arising from the application of theory 

 has not been carefully eliminated from the pages, as 



