August i8, 192 i] 



NATURE 



795 



(Canada Geol. Survey, Mem. ii8, 1920). R. Lockhart 

 Jack, in "The Salt and Gypsum Resources of South 

 AustraUa " (Geol. Surv. S. Australia, Bull. 8, 192 1) 

 interestingly connects the salt of the lagoons of the 

 Yorke Peninsula, between Spencer Gulf and the Gulf 

 of St. Vincent, with "cyclic" salt imported aerially 

 during long ages from the sea. The supply thus given 

 to the soil is drawn on bv the lakes, with, of course, 

 some addition from salt-dust now falling on their sur- 

 faces, and depends on conditions of dryness, whereby 

 the local water-table does not rise dangerously high. 

 The meteorological features of the region are well put 

 forward. The deposits of gypsum are similarly attri- 

 buted to cyclic matter, which has been redissolved 

 and carried by the saline ground-waters (p. 90) into 

 lake depressions. On the margins of these it eva- 

 porates and becomes blown up into dunes. There are 

 also some occurrences of gypsum in a more normal 

 and less interesting manner in Cainozoic rocks. 



The graphite deposits of the world outside the 

 United States are reviewed, with maps, in a valuable 

 paper by A. H. Redfield (" Foreign Graphite in 1919," 

 U.S. Geol. Surv., Min. Resources, 1919, part ii., 

 No. 12, 192 1). This pamphlet should stand beside 

 our text-books of mineralogy, which constantly require 

 the refreshing influence of general surveys of this 

 nature. Though the commercial aspect is naturally 

 paramount, the names of localities and the references 

 to literature will be of service to the student. 



The work of R. E. Liesegang has added consider- 

 ably to the interest of zoned and banded deposits. 

 P. A. Wagner (Trans. Geol. Soc. S. Africa, vol. xxiii., 

 p. 118, 1921) describes the "Nature and Origin of the 

 Crocodile River Iron Deposits " in the Rustenburg 

 district of the Transvaal. He compares them with 

 those of the Lake Superior region, and holds that the 

 haematite and hydroxide masses are concentrations by 

 downward percolation from beds of siderite and ferru- 

 ginous chert. In some cases alteration in place has 

 led to the formation in chert of magnetite, haematite, 

 or brown hydroxide, alike pseudomorphous after 

 rhombohedral siderite. 



Olaf Holtedahl (Amer. Journ. Sci., vol. cci., p. 195, 

 192 1) reviews old and recent wofk on the zoned con- 

 cretions of calcite in the magnesian limestone of | 

 Durham, pointing out the reasons that have led Eng- | 

 lish geologists to regard them as mineral structures ; 

 arising through secondary alteration. Their resem- ; 

 blance to some of the pre-Cambrian structures 

 claimed by Walcott as algal (Camasia, Newlandia, 

 Greysonia, etc.) inspires the author with caution in 

 dealing with these older specimens. 



Mineralogists cannot afford to overlook the paper 



by F. W. Clarke and W. C. Wheeler on "The In- 

 organic Constituents of Marine Invertebrates " (U.S. 

 Geol. Surv., Prof. Paper 102, 1917) with its important 

 series of analyses of the hard parts of a wide range 

 of living creatures. The proportion of magnesium 

 carbonate to calcium carbonate bears, of course, on 

 the much-discussed origin of dolomite, and it is shown 

 that organisms capable of depositing calcite may 

 accumulate magnesium by isomorphous substitution » 

 while this cannot take place when the hard parts are 

 formed of aragonite. The utilisation of magnesiun> 

 is very distinctly favoured by warm conditions, speci- 

 mens from Arctic or Antarctic waters, or from very 

 deep waters, showing relatively small proportions^ 

 Crinoids, for instance, from 47° N. lat. and a depth 

 of 1000 metres may yield 9 per cent, -of magnesiunt 

 carbonate, while 12 per cent, commonly occurs at 

 similar depths near the equator. A biological problem: 

 of much interest is here opened. No such authorita- 

 tive and detailed analyses have hitherto been avail- 

 able. As was already known, alcyonaria generally 

 are rich in magnesium carbonate. An equatorial 

 specimen of Phylhygorgia quercifolia is here shown to 

 contain 1573 per cent. The influence of these facts 

 on determinations of specific gravity in fossil forms 

 should, of course, be noted. 



The rhyolites of Lipari, including the familiar 

 obsidian of the Rocche Rosse, have received com- 

 plete and critical examination and analysis frora 

 H. S. Washington (Amer. Journ. Sci., fourth series, 

 vol. 1., p. 446, 1920). It is shown that in the glassy 

 varieties ferrous oxide predominates largely over 

 ferric oxide, while this condition is reversed in crystal- 

 line types. It is suggested that the glassy state 

 retains more nearly the constitution of the igneous 

 magma, while oxidation occurs as the gases are per- 

 mitted to escape. 



W. R. Browne provides a new study of differentia- 

 tion in an igneous mass, through the sinking of 

 crvstals and later extrusions, in his description of 

 "The Igneous Rocks of Encounter Bay, South Aus-. 

 tralia " (Trans. Roy. Soc. S. Australia, vol. xliv., 

 p. I, 1920). In the same volume, p. 300, W. Howchin 

 reviews coarse fragmental structures of various kinds; 

 in rocks, citing Australian examples, and he usefully 

 directs attention to the influence of desiccation in 

 breaking up a sediment in an early stage of its his-, 

 torv. The drying mud of lakes is an example. Atten-. 

 tion mav be directed to the moderate price (10s. 6d.)< 

 of this volume and of some other illustrated publica- 

 tions from our federated Commonwealths, in the hope 

 that the enterprise displayed may react on issues ins 

 the homeland. G. A. J. C. 



Plant Pests and their Control. 



By Dr. William B. Brierley. 



THE "Report on the Occurrence of Insect and 

 Fungus Pests on Plants in England and Wales 

 for the Year 1919," ' which has just been issued by 

 the Intelligence Department — Plant Pests Branch of 

 the Ministry of Agriculture and Fisheries, marks a 

 very definite step in the recognition in this country 

 of the danger to our food crops from diseases caused 

 bv insects, fungi, bacteria, etc. This disease-survey 

 work was originated bv a sub-committee of the 

 Technical Committee of the late Food Production De- 

 partment, which was formed to advise the department 



1 Ministry of Agriculture and Fisheries. Intelligence Department: Plant 

 Pests Branch. (Miscellaneous Publications, No. 33.) " Report on the 

 Occurrence of Insect and Fungus Pests on Plants in England and Wales for 

 the V^ar 1919." Pp. 68. (London : H.M. Stationery Office, igai.) is. (sd. 



NO. 2703, VOL. 107] 



on questions relating' to plant disease and insect pests.. 

 A few honorary correspondents scattered throughout 

 the country forwarded monthly statements relating to- 

 diseases and pests in their own particular areas, and' 

 at the close of the year these were summarised by 

 the sub-committee, and a "Report on the Occurrence- 

 of Insect and Fungus Pests during 1917 " was pub-, 

 lished. This was the first time that any successful 

 attempt had been made to g-ather together and' 

 systematise data relating to the incidence and spread 

 of plant disease in this country. With the experience- 

 gained the work was continued in a more efficient 

 manner, and a report for 1918 issued. There has now 

 appeared the present, and somewhat belated, report 

 for 19x9, and a comparison of these three publications; 



