Nov. 4, 1880J 



NATURE 



to sudden shocks or slow disruption, were produced with 

 such irresistible force as to preserve their linear character 

 and parallelism through rocks of the most diverse nature, 

 and even across old dislocations having a throw of many 

 thousand feet. Yet so steadily and equably did the 

 fissuring proceed over this enormous area, that compara- 

 tively seldom was there any vertical displacement of the 

 sides. We rarely meet with a fissure which has been 

 made a true fault with an upthrow and downthrow side. 



The ne.xt feature is the rise of molten basalt up these 

 thousands of fissures. The most voluminous streams of 

 lava that have issued from any modern volcanic cone 

 appear but as a minor manifestation of volcanic activity 

 when compared with the filling of those countless rents 

 over so wide a region. Mining operations in the Scottish 

 coal-fields have shown that dykes do not always reach 

 the surface. In all parts of the country, too, examples 

 may be observed of breaks in the continuity of dykes. 

 The same dyke vanishes for an interval and reap- 

 pears on the same line, but is doubtless continuous 

 underneath. What proportion of the dykes ever commu- 

 nicated with the surface at the time of their extravasation 

 is a question that may perhaps never be answered. It is 

 difficult to believe that a considerable number of them 

 did not overflow above ground even far to the east of the 

 main and existing outflows. But so extensive has been 

 the subsequent denudation that all trace of such super- 

 ficial emission has been removed. The general surface of 

 the country has been lowered by sub-aiirial waste several 

 hundred feet at least, and the dykes now protrude as hard 

 ribs of rock across the hills. 



Traced westwards the dykes increase in abundance, 

 till at last they reach the great basaltic plateaux. Mac- 

 cuUoch long ago sketched them in Skye, rising through 

 the Jurassic rocks and merging into the overlying sheets 

 of basalt. Similar sections occur in the other islands 

 and in the north of Ireland. The lofty mural escarp- 

 ments presented by the basalt plateaux once extended 

 far beyond the limits to which they have now been 

 reduced. The platform from which they have been re- 

 moved shows in its abundant dykes the fissures up which 

 the successive discharges of lava rose to the surface, 

 where they overflowed in wide level sheets like those still 

 so fresh and little eroded in Western North America. 



That there were intervals between successive out- 

 pourings of basalt is indicated by the occasional inter- 

 stratification of seams of coal and shale bet.veen the 

 different flows. These partings contain a fragmentary 

 record of the vegetation which grew on the neighbouring 

 hills and which may even have sometimes found a foot- 

 hold on the crumbling surface of the basalt floor until 

 overwhelmed by fresh floods of lava. Not a trace of 

 marine organisms has anywhere been found among these 

 interstratifications. There is every reason to believe that 

 the volcanic eruptions were all subal-rial. Sheet after 

 sheet was poured forth over the wide valley between the 

 mountains of Donegal and the Outer Hebrides on the 

 one side and those of the north-east of Ireland and the 

 Avest of Scotland on the other, until the original surface 

 had been buried in some places 3000 feet beneath volcanic 

 ejections. 



I believe that the most stupendous outpourings of lava 

 in geological history have been eftected not by the 



familiar type of conical volcano, but by these less known 

 fissure-eruptions. Both types are of course only manifesta- 

 tions in different degrees of the same volcanic energy-. It 

 is by no means certain that the " massive" or fissure type 

 belongs wholly to former geological periods. In particular 

 one is disposed to inquire whether the great Icelandic 

 lava-floods of i783^the most voluminous on record — may 

 not have been connected rather with the opening of wide- 

 reaching fissures than with the emissions of a single 

 volcanic cone. The reality and inrportance of the 

 grander phase of volcanism marked by fissure-eruptions 

 have been recognised by some of the able geologists 

 who in recent years have explored the Western States and 

 Territories of the American Union. But they have not 

 yet received due acknowledgment on this side of the 

 Atlantic, where the lesser type of cones and craters has 

 been regarded as that by which all volcanic manifesta- 

 tions must be judged. We are fortunate in possessing 

 in the north-west of Europe so magnificent an example 

 of fissure-eruptions, and one which has been so dissected 

 by denudation that its whole structure can be interpreted. 

 The grand examples on the Pacific slope of America 

 have yet to be worked out in detail, and will no doubt 

 cast much fresh light on the subject, more especially upon 

 those phenomena of which in Europe the traces have been 

 removed by denudation. But the other continents also 

 are not without their illustrations. The basaltic plateaux 

 of Abyssinia and the " Deccan traps " of India probably 

 mark the sites of some of the great fissure-eruptions 

 whidi have pioduced the lava-fields of the Old World. 

 In their recent admirable rcsttiui! of the '•' Geology of 

 India," Messrs. Medlicott and Blanford describe the per- 

 sistent horizontality of the vast basalt-sheets of the 

 Deccan, the absence of any associated volcanic cones or 

 the least trace of them in that region, and the abundance 

 of dykes in the underlying platform of older rocks 

 where it emerges from beneath the volcanic plateaux. 

 They confess the difficulty of explaining the origin of such 

 enormous outpourings of basalt by reference to any modern 

 volcanic phenomena. Their descriptions of these Indian 

 Cretaceous lava-floods might, however, be almost literally 

 applied to the Miocene plateaux of North-western Europe 

 and to the Pliocene or recent examples of Western North 

 America. Arch. Geikie 



THE ATOMIC THEORY 

 The Atomic Theory. By Ad. Wurtz, Merabre de 

 rinstitut, &c. Translated by E. Cleminshaw, M.A. 

 (London : C. Kegan Paul and Co., 18S0.) 



T'^HE latest addition to the International Scientific 

 Series is at once a scientific treatise and an artistic 

 work. The translator has very fairly maintained the 

 clearness and crispness of the French style, whereby the 

 book is marked with a distinct individuality and self- 

 completeness. 



The sharpness of the impression which this work pro- 

 duces on the mind is gained without making any great 

 sacrifice of accuracy, although it must be confessed there 

 is, in some chapters, a lack of detailed facts, which is 

 against the value of the work as a reference book for the 

 advanced student ; and in others there is too free a use 

 of fancy, which faculty is not synonymous with that 



