May 2, 1918] 



NATURE 



^75 



31 per cent, of albite. The author compares this with 

 recorded occurrences of albite in Jurassic and other 

 unmetamorphosed limestones in Euiope. Issel's dis- 

 covery {Coinptes rendiis, February 24, i8go) of albite 

 crystals enclosing radiolaria in a Cainozoic limestone 

 may be added to those quoted. Prof. Daly concludes 

 that the alkaline felspars of Waterton crystallised out, 

 nice the European examples, at the sea-floor, or soon 

 after the burial of the associated dolomite, and at 

 temperatures which may have been well under 100" C. 

 Time, he points out, may be an important factor, and 

 this has to be borne in mind in experimental work on 

 such productions. 



Mr. W. A. Tarr {Amer. Journ. Sci., vol. xliv., 

 p. 409, 1917) has examined with much care the 

 elongated chert-lumps in the Burlington Limestone of 

 Missouri, a formation of Lower Carboniferous age. 

 Because he finds no remains of siliceous organisms 

 associated with the chert, and only a partial replace- 

 ment of originally calcareous fossils, he criticises the 

 view that flint is commonly a pseudomorph of portions 

 of the limestone in which it occurs, and remarks that, 

 had the first investigations been made on material 

 collected in Missouri, the theory that attributes the 

 material of flint in other cases to the solution of 

 organic remains would not have been propounded. 

 This shows that the author attaches little weight to 

 the mass of evidence collected outside Missouri ; yet his 

 reading has evidently been extensive. No reference is 

 made to the frequent occurrence of silicified oolitic 

 rocks, from the Assynt Limestone upwards, in which 

 all the structure of the original limestone is retained, 

 nor to the remarkable suggestion made by R. Liese- 

 gang as to the rhythmic deposition of flint layers by 

 water holding silica in solution. Mr. Tarr does well 

 to emphasise the fact that flint formation goes on at an 

 early stage in the consolidation of limestone, since 

 pebbles of the flint are often found in the next follow- 

 ing deposits ; but it does not follow from this that flint 

 nodules represent gelatinous matter precipitated directly 

 on the sea-floor. The shrinkage-cracks in the Missouri 

 flint, filled by limestone, and Mr. Tarr's interesting 

 experiments on the precipitation of silica, help towards 

 his conclusion that the flint in the Burlington Lime- 

 stone is not a replacement of the calcareous rock ; 

 but this by no means disposes of the cases where flint 

 masses spread out into successive layers of a lime- 

 stone, or of the thousands of sections from Cretaceous 

 or Carboniferous material that are stored in European 

 collections. We read this paper with the feeling that, 

 if Mr. Tarr has proved his case for the Missouri 

 example^ he has dealt with an exceptional occurrence 

 which certainly deserved description. 



It is characteristic of the association of the sciences 

 in technical industries that geologists should be asked 

 to look for "pulpstones." Mr. L. H. Cole has, in 

 consequence, tested certain Canadian sandstones "to 

 determine their suitability as pulpstones " (Canada, 

 Dept. of Mines, Mines Branch, Bull. 19, 1917). These 

 are used in wood-pulp mills, and should tear the fibres 

 apart rather than cut them. In the case of sandstones, 

 the grains should be of medium size and medium 

 angularity, and the stone must resist considerable 

 stresses. Diagrams of the grinding machines add in- 

 terest to this useful bulletin. , 



Mr. H. Ries describes a gritty plastic "clay" re- 

 sembling loss (Amer. Journ. Set., vol. xliv., p. 316, 

 1917), which proves to consist of 985 per cent, of small 

 crystals of dolomite and 1-5 per cent, of iron oxide 

 and alumina. He suggests that the flat faces of the 

 dolomite rhombs, coming into contact or separated 

 onlv by a film of water, may account for the plasticity, 

 surface tension holding the grains together, but allow- 

 ing of slipping along their faces. 

 NO. 2531, VOL. lOl] 



The phosphate deposits of Saldanha Bay, north-west 

 of Cape Town, have been reported on by Dr. A. L. 

 Du Toit (S. Africa Geol. Survey, Mem. 10, 1917). 

 The material contains from 10 to 22 per cent, of phos- 

 phoric oxide; but this is mostly combined with 

 aluminium and iron, having been produced by the 

 action of ancient guanos on underlying granitic rocks. 

 The author discusses the value of such phosphates as 

 fertilisers, making no attempt in his summary to 

 reconcile the somewhat contradictory statements of 

 agricultural chemists, but pointing out the need for 

 experiments on natural lines under biochemical condi- 

 tions. His proper mistrust of Germany should not 

 have led him into the error of asserting that the citric 

 acid test of availability of phosphorus was " devised in 

 Germany for the purpose of enabling that country to 

 supply the markets of the world with highly citric- 

 soluble basic slag." 



Mr. T. A. Jaggar, jun. (Journ. Washington Acad. 

 Sci., vol. vii., p. 277, 1917), describes the phenomena 

 presented by the aa and pahoehoe types of Hawaiian 

 lava during the cooling of the mass. He suggests 

 that the quantity of confined gas for each unit of 

 volume of melt may be a controlling factor. The ex- 

 pansion of gas in the aa type may be more rapid, but 

 " with so many variables there is no cause for wonder 

 that the distinction is as yet unexplained." The author 

 proposes the term " dermolith " for the pahoehoe type, 

 which has a crust or skin as its chief character, and 

 the term "aphrolith" (foam-stone) for types of lava 

 which divide on the surface, like aa, into lumpy vesi- 

 cular unit:5. He prefers "lith" to "lite" as a ter- 

 mination, on the well-established analogy of "mono- 

 lith." 



Prof. R. A. Daly has furnished a useful synopsis 

 of our knowledge of the nature of rocks in the Pacific 

 islands (Bull. Geol. Soc. America, \ol. xxvii., p. 325) 

 and urges that much more observation is required. 

 He believes that, so far as can be judged at present, 

 the primary magma under the Pacific is of basaltic 

 composition, giving rise to andesites and picrites by 

 difi'erentiation, and to alkaline rocks by solution of 

 comparativelv small proportions of limestone. 



G. A. J. C. 



THE BIRD CULT OF EASTER ISLAND. 



IN the issue of Folk-lore for December last Mrs. 

 Scoresby Routledge gives a singularly interesting 

 account of the bird cult of Easter Island. The sacred 

 bird is the sooty tern {Sterna fuliginosa), and the 

 valued privilege of securing the first egg is a matter 

 of competition between members of the Mata-toa 

 group, the right to become a competitor being acquired 

 only by supernatural agency. The selection is made 

 through a dream vouchsafed to a divinely gifted indi- 

 vidual, the Iviatua. The candidate on selection takes 

 a new name, and the bird-name thus conferred was 

 given to the year in which victory was achieved, thus 

 forming an easily remembered system of chronology. 

 It is also significant that this bird cult is connected 

 with the statues for which the island is famous. The 

 bird^man used to spend his official year on the moun- 

 tain in which the monoliths were quarried ; the bird 

 initiation of children was also performed in connec- 

 tion with the statues, and the ring design on the back 

 of the images was reproduced at the ceremony on the 

 children's backs. There seems reason to believe, says 

 the writer, that the people who originally celebrated 

 the bird cult included in it reverence for the statues. 

 The ancestors of the present inhabitants were, there- 

 fore, either the makers of the monoliths of Easter 

 Island, or, if the bird worshippers represent a more 



