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76 



NATURE 



[September 22, 1910 



substances in the case of weathered rocks, and he here 

 opens up a new field, which will, we hope, be promptly 

 cultivated. 



M. G. C^saro {Bull, classe des Sci., Acad. roy. de Bel- 

 _gique, 1909, p. 435) has made a comprehensive study of the 

 mesotype group of zeolites, including a mesolite from 

 Kenbane Head, co. Antrim (p. 447), once alleged to be 

 galactite. The author (p. 492) ultimately concludes that 

 galactite is a mixture of natrolite and scoiezite. 



A new light is thrown on nephrite by Prof. Steinmann 

 ^Sitsungsber. nicdcrrhcin. Gcsell. Nat. u. Hcilkundc m 

 Bonn, 1908, pub. 1909, p. i), who concludes that the 

 I^igurian examples were originally dykes in the surround- 

 ing olivine-rocks, and had the composition of websterite or 

 ■diopside-rocks. The expansion of the peridotites, due to 

 serpentinisation, caused pressures throughout the mass, and 

 the dykes became converted into the schistose nephrites that 

 now remain. The brecciated and slickensided character 

 common in serpentine-rock is aptly accounted for by this 

 chemical expansion. " Schwellungsmetamorphosc " (p. 13) 

 is introduced as an appropriate term, and Steinmann holds 

 that the Ligurian serpentines received their main mineral 

 characters before the occurrence of the great movements 

 that folded them in among the Alps. 



This paper, connecting mineral changes and large rock- 

 jnasses, may lead us on to igneous rocks in general. Mr. 

 R. A. Daly (Proc. Amer. Acad. Arts and Sci., vol. xlv., 

 1910, p. 211) has sought to establish the average chemical 

 compositions of igneous-rock types, and his results, largely 

 based on Osann's collection of modern analyses, are likely 

 to serve as standards for all who use ordinary rock-names. 

 The number of analyses employed is shown in each case, 

 and we are naturally left to presume that no very widely 

 differing types are included here under the same name. A 

 second series of averages is generously given, in which the 

 figures are re-calculated with water omitted. Mr. Daly 

 (p 236) urges that Rosenbusch's classification, as here 

 emphasised, is objective and natural in a hig^hly useful 

 ■degree. Comparisons can now be easily made, by using 

 these tables, between rocks of different grain, and the 

 author points out that dacite is the effusive type of 

 *' granodiorite," rather than of the far less siliceous quartz- 

 diorites of our ordinary terminology. On p. 240 we find a 

 characteristic suggestion as to the cause of the similarity 

 of composition of rocks of various degrees of antiquity, 

 since " in general, differentiation in batholiths, when well 

 advanced, restores the condition temporarily disturbed by 

 jiiagmatic assimilation." 



Mr. G. P. Merrill (_Amer. Journ. Sci., vol. xxvii., p. 469) 

 concludes from averages of analyses of stony meteorites, 

 compared with those of terrestrial rocks, that magmatic 

 differentiation could not have produced our rocks from 

 planetesimal material of meteoritic composition. But he 

 does not quite touch the main question, though he goes 

 near it (p. 470). Surely the rocks of our crust are an 

 extremely thin film on an interior of unknown composition. 

 A planet like the earth, when duly disrupted, would supply 

 exceedingly little material of the kind familiar to the 

 geologist, and a vastly preponderating mass of far more 

 basic character, .i^ons might go by before a chip of the 

 crust fell upon another planet. Moreover, have not the 

 glassv globules found in the superficial deposits of Bohemia 

 (Bouteillenstein and Moldavite) been claimed by a high 

 authority as of meteoritic origin? 



Mr. R. T. Chamberlin. while keeping his eye on 

 planetesimalf, has published through the Carnegie Institu- 

 tion a paper on "The Gases in Rocks," in which a large 

 amount of new material is made available. In the course 

 of experiments, most gas arises from rocks that contain the 

 greatest proportion of ferromagnesian minerals (p. 27). 

 The discussion of the condition of the gases that are found 

 to exist in rocks covers ground of great interest to 

 geologists. The author aflirms, with Suess, that the water 

 and gases of the interior (p. 6q) " form an integral part in 

 the magmas, having been vital factors in their development 

 from the primitive planetary matter." Lavas, it is urged, 

 originate far below the possible reach of surface-waters 

 (d. 73), and thus bring up original water with them. On 

 the other hand. Dr. Johnston-Lavis (" Mechanism of Vol- 

 canic Action," Geol. Mai;., I90q, p. 437) continues to urge 

 that the water found in lavas is absorbed by them as they 



NO. 2134, VOL. 84] 



rise into the moist layers of the upper regions of the crust. 

 Mr. R. A. Daly (Journ. of Geology, vol. .xvi., p. 401), 

 in a paper on the origin of augite-andesite, supports the 

 views of Scrope and Darwin on the differentiation of an 

 igneous magma by fractional crystallisation. His views 

 are quoted several times, under the name of Daley, in a 

 remarkable paper by Dr. H. I. Jensen, on the distribu- 

 tion, origin, and relationships of alkaline rocks (Proc. 

 Linn. Soc. N.S.W., vol. xxxiii., p. 491). The rather 

 dubious term " alkaline " is here used to denote " rich 

 in combined alkalies," and the rocks discussed are those 

 that might be conceived to originate by differentiation 

 from a foyaite-magma. Dr. Jensen examines their dis- 

 tribution in space and time, and concludes that they are 

 almost all associated with Cainozoic earth-movements. 

 The Christiania series (p. 502) is merely known to be 

 post-Silurian, and may therefore be Eocene. " Alkaline 

 rocks are continental and occur in areas of normal fault- 

 ing above and possibly shear below " (p. 515). They are 

 attributed to the melting and assimilation of sediments 

 rich in alkalies (such as were formed when our earth's 

 surface first cooled below 100° C), as they gradually sank 

 under the weight of Pala;ozoic and Mesozoic deposits. The 

 crustal re-adjustments of the Eocene period allowed them 

 to be expelled within the low-pressure regions, i.e. the 

 continents, towards which they had gradually flowed. 

 There is much more in this paper than might appear from 

 so generalised a summary. Dr. Jensen's thorough study 

 of the types of rock with which he deals is evidenced by 

 several papers on their occurrence in eastern Australia, 

 published in the last two years (Linn. Soc. N.S.W. and 

 .Australasian Association for the Advancement of Science, 

 1908-9). 



Messrs. A. Boudariat and Johnston-Lavis (Bull. Soc. 

 Beige de Gio]., tome xxii., 1909, p. 103) describe the 

 occurrence of a basalt in the volcanic cone of Tritriva in 

 central Madagascar, which has enriched itself with 

 abundant grains of quartz at the expense of an underlying 

 gneiss. The quartz-grains show the aureole of augite that 

 is so common round inclusions ef quartz in basic rocks. 

 .At Tritriva the volcanic chimney that was blown through 

 the gneiss is clearly visible, and Dr. Johnston-Lavis makes 

 some just remarks on the analogy with the so-called 

 quartz-basalts of other areas, and on the modification of 

 lavas by absorption. 



Mr. C. B. Travis (Proc. Liverpool Geol. Soc, vol. x., 

 p. 311) has examined the Ordovician rhyolites of Nant 

 Ffrancon, Carnarvonshire, and gives good reason for 

 agreeing with Iddings and Parkinson that lithophysal 

 cavities, such as those traceable in the large Welsh 

 spherulites, were original features of the lavas. The view 

 that all such cavities are due to decomposition of solid 

 structures was abandoned, however, by its supporters so 

 far back as 1S92. 



The petrology of sedimentary rocks still attracts few 

 workers. Dr. Woolacott (Univ. Durham Phil. Soc, 

 Memoir i., 1909) describes a brecciated magnesian lime- 

 sCone in a paper illustrated by views of the rock as it 

 occurs in the open field. Experiment (p. 5) leads to an 

 estimate of the thrust concerned as having generated a 

 pressure of 300 tons to the square foot. Mr. G. Linck, 

 so well known for his researches on chemically deposited 

 limestones, contributes a lucid paper on these rocks to the 

 Naturwi.'isenschaftliche Wochcnschrift, 1909, p. 6S9. The 

 Canadian Mining Institute publishes (Journ., vol. xii., 

 1909) a general paper by Mr. E. Coste on petroleums 

 and coals, strongly supporting the "solfataric " view of 

 the origin of petroleum. Mr. .\. J. Cox (Philippine Journ. 

 Sci., vol. iii., p. 301) investigates the Philippine coals as 

 fuels, and concludes that they may compete successfully 

 with those of Australia. This subject is also dealt with 

 by Mr. W. D. Smith (" Mineral Resources of the Philip- 

 pine Islands," Bureau of Science of Manila, 1909). 

 Barytes is so frequent as a cementing material in rocks 

 that Dr. Trener's discussion of its origin in mineral waters 

 rising from below is of general petrological interest 

 (Jahrb. k.k. Rcichsanstalt, Bd. Iviii., p. 439). 



.As regards the petrography of special areas, we may 

 note the excellent " Introduction to Petrography and the 

 Collections of Rocks " published by the Royal Scottish 

 Museum, Edinburgh (1909, price id.). Emphasis is here 



