September 2, 1922] 



NA TURE 



globe, still more emphasised by the recent discovery 

 of one of the species, Cardita [= Venericadid] plani- 

 costa, in Peru (Nature, April 29, 1922, p. 561). 



The Origin of Igneous Rocks rich in Alkalies. 

 —Dr. S. J. Shand (" The Nepeline Rocks of Sheku- 

 kuniland," Trans. Geol. Soc.S. Africa, vol. xxiv. p. 11 1, 

 1921), discusses an occurrence of the so-called alkaline 

 igneous rocks in and around the farm Spitzkop in the 

 Transvaal. Following the work of N. L. Bowen, he 

 holds that the original magma separated during cool- 

 ing into a norite and a mass rich in alkalies. The 

 latter rose towards the surface through the well-known 

 dolomite formation, and floated up a huge mass of 

 limestone, which has a visible area of half a square 

 mile. By reaction with the limestone, as R. A. Daly 

 has urged in other cases, a nepheline-syenite (foyaite) 

 magma was produced, which becomes much more 

 calcareous in the neighbourhood of the limestone. 

 The author furnishes a good review of the whole 

 question in "The Problem of the Alkaline Rocks" 

 (Proc. Geol. Soc, S. Africa, 1922, p. xix). He defines 

 an alkaline rock by pointing out that in common 

 igneous rocks the alkali-metals [does he not mean 

 their oxides ?] " are combined with alumina and silica 

 in the molecular proportion of 1:1:6 (in felspars) 

 or 1 : 3 : 6 (in micas). An alkaline rock, if names are 

 to mean anything, should be one in which the alkalies 

 are in excess of the 1:1:6 ratio, either alumina or 

 silica or both being deficient." He then discusses 

 the work of N. L. Bowen, who, since the publication 

 of Shand 's paper, and in association with G. W. Morey, 

 has shown that orthoclase, at about 1200 , does not 

 melt as a whole, but yields leucite and a glass (Am. 

 Journ. Sci., vol. cciv. p. 1, 1922). Bowen and Morey 

 point out that leucite may thus arise as a temporary 

 mineral in cooling granite magmas ; since it breaks 

 up into orthoclase and nepheline, the characteristic 

 minerals of the nepheline-syenites may arise in 

 association through this intermediate phase. 



Birds marked in Europe recovered in South 

 Africa. — In the August number of British Birds Mr. 

 H. F. YVitherby records the recovery at Jansenville, 

 Cape Province, on January 8, 1922, of a swallow 

 ringed as a nestling in Berkshire on August 20, 1921. 

 Details of the five previous records of the kind are 

 recapitulated, with a useful map, but these have 

 already been quoted in Nature in Dr. Thomson's 

 recent article (March 16, vol. 109, p. 346) on the 

 migrations of British swallows. In the same publica- 

 tion Mr. W. L. Sclater directs attention to a record 

 of a common tern marked in East Prussia and 

 recovered in Natal ; another common tern marked in 

 Sweden has been recovered in Cape Province, while 

 there is also a remarkable record of one marked in 

 Maine, U.S.A., and recovered in West Africa. Apart 

 from these six swallows and two terns, the only birds 

 which appear to have been recorded by the marking 

 method as travelling from Europe to South Africa 

 are white storks : there are many such records of this 

 species, which has been largely marked in Hungary, 

 Germany, and Denmark, and there are also several 

 very valuable records from intermediate localities 

 such as Central Africa. The records of European 

 marked birds recovered in Northern Africa are less 

 restricted as to species and include cases of the lap- 

 wing, lesser black-backed gull, starling, swallow, and 

 white stork. 



Attack on a Moth by a Wasp. — Miss M. M. 

 Buchanan sends us from Penrith a specimen of a moth 

 which was caught while fluttering near the ground 

 with a wasp attached to its thorax. The wasp escaped, 

 but one from a nest a couple of yards away was 

 Vespa vulgaris, Linn., and the moth was a small 



Emerald moth (Geometra vernaria, Hiibn.). Wasps, 

 which, as is well known, are almost omnivorous, 

 are in the habit of seizing and carrying off other 

 insects as food for their larvae, but their chief victims 

 belong to the order Diptera (two-winged flies). 

 Major E. E. Austen, of the Natural History Museum, 

 informs us that he has personally witnessed an attack 

 by a wasp on a Drone-Fly (Eristalis tenax, Linn.). 

 In this case, in spite of the fact that the victim was 

 the bulkier insect of the two, the wasp flew away with 

 the bod}' of the fly in a very few moments, after first 

 ruthlessly cutting oft by means of its powerful 

 mandibles the right wing, the head, and lastly the 

 left wing, all of which from the wasp's point of view 

 were evidently useless encumbrances. Since wasps 

 are diurnal in habit, and moths, speaking generally, 

 are the reverse, attacks by the former upon the latter 

 can scarcely be of common occurrence, and the 

 incident described by Miss Buchanan, if not unique, 

 is certainly unusual. 



Nigerian Plants of Economic Value. — Part IV. 

 of " The Useful Plants of Nigeria," published as 

 Additional Series IX. of the Kew Bulletin, completes 

 the work begun in 1908 by Mr. J. H. Holland in 

 collating the information of plants of economic im- 

 portance in Upper Guinea. The remainder of the 

 dicotyledons and the monocotyledons are considered, 

 and a brief note is given on the ferns and fungi. 

 Bound with this part is an appendix containing a 

 list of books of general interest on West Africa, a 

 complete index to all four parts, an introduction, and 

 a preface. Sir David Prain, in the introduction, 

 states brieflv the reasons which led to the work being 

 undertaken and the selection of Air. Holland, from 

 his experience of Nigeria, as compiler. In the preface, 

 Mr. Holland outlines the arrangement and scope of 

 the work. Among the natural families reviewed in 

 this part, the Euphorbiaceas and Moraceae provide 

 many plants of economic importance. Under the 

 monocotyledons, valuable information is brought to- 

 gether concerning, among others, the banana, pine- 

 apple, sisal hemp, yams, cocoyams, piassava, oil palm, 

 and coconuts. The pages on the Gramineae and the 

 information on fodder grasses are particularly wel- 

 come at a time when stock-raising is receiving so 

 much consideration on the Coast. The list of refer- 

 ences to special works and monographs given at the 

 end of each species will be found very useful, but in 

 the illustrations cited, reference to a typical example, 

 easily accessible, would have saved much space and 

 rendered the work more handy. The increased price 

 of this last part raises the cost of the whole work to 

 il. 8s., and may prevent it becoming as popular as 

 it should be. Mr. Holland is to be congratulated on 

 bringing this compilation to so successful a conclusion. 

 It has entailed many years of careful research, and 

 it fills an important gap in our reference books on 

 West Africa. 



Tidal Investigations. — The third annual report 

 of the Tidal Institute of the University of Liverpool 

 recounts briefly a number of tidal investigations 

 which have been begun there, but not completed, 

 during the past year. The first two years' work 

 established the existence of important residual 

 fluctuations of sea-level, both periodic and irregular, 

 which remain after all those harmonics directly account- 

 able for by the astronomical forces have been removed. 

 Two hypotheses which give some promise of explain- 

 ing the periodic part of these residuals have been 

 examined, but it is intended to apply further tests 

 before publishing an account of the work. The main 

 investigations of the year relate, however, to the 

 irregular variations of sea-level due to meteorological 

 causes. The method of intensive tidal analysis 



no. 2757, VOL. r 10] 



