W. 2, 1876] 



NATURE 



tolos^ische Reichsanstalt j and under these circumstances 



f. Zittel of Munich has pointed it out to the author of 



present paper as a promising field of study. Mr. 



>ale's work will certainly be of considerable use to future 



■xplorers of the district, though not carried out in sufficient 



»tail to warrant, in his own case, any very important 



jeneralisations. Indeed, the memoir consists almost wholly 



le »f transcriptions of notes and rough drawings of sections 



•elating to a number of different localities which are indi- 



ated by reference to a key-map. The author's general 



Conclusions, so far as they go, are shown in a very clear 



1 useful table, from which it appears that at this point 



Jie Alps, the Jurassic and Rhaetic strata (including in 



iK former the Tithonian) have a united thickness of from 



000 to 7,000 feet. Vast as is the estimate, no one ac- 



juainted with this or the surrounding districts will be 



r.clined to regard it as excessive. 



Mr. Dale has evidently made good use of his oppor- 



-ities, so far as they have gone, and has given us in this 



ncmoir the results of a piece of well-directed observation. 



: '.\'e hope to have further details from his pen concerning the 



^iame interesting region. The list of errata, which is rather 



_ long for a memoir of the proportions of the present, does 



pot by any means exhaust the whole of the printer's errors. 



We are tempted to fear that Mr. Dale is not sufficiently 



,j :areful in keeping so distinct from one another, as behoves 



"^ 1 working geologist, his notes relating to various subjects ; 



For, by some strange chance a stray page of a sermon seems 



:o have fallen into the hands of the compositor and to 



irs have been set up by him at the end of the author's gcolo- 



iK logical notes. J. W. J. 



tdi 



\\ LETTERS TO THE EDITOR 



•\The Editor does not hold himself responsible for opinions expressed 

 '*jj by his correspondents. Neither can he undertake to return, 



or to correspond with the xvriters of rejected manuscripts. 



No notice is taken 0/ anonymous communications.'] 



"Geographical Distribution of Animals" 

 T FIND that Mr. Wallace in his new work on the " Geogra- 

 al Distribution of Animals " when stating the limits of his 

 ->lon sub-region (vol. i. p. 327), gives among mammals the 

 genus Tut>aia and among birds "a species of J/v/«//4^«/<r, whose 

 nearest ally is in Java " as characteristic of that sub-region. 

 Further, in the tabular statement (vol. ii. p. 187), Tupaia is 

 altogether omitted from the Indian sub-region. 



It is not my intention to enter here into the general question 

 njof the divisions of the oriental region which Mr. Wallace has 

 a adopted. The subject has I know been undertaken by at least 

 iiifone well-known Indian naturalist. My object at present is 

 iisimply to record the fact that I have found both Tupaia Elliotli 

 fo and Myiophonus Honfieldi ranging together far to the north of 

 i; the limits given by Mr. Wallace for his Ceylon sub-region. 



Tupaia I first met with at an elevation of about 1,500 feet in 

 tl.e Sutpuru Hills, near the Pachmari plateau in the Central 

 Provinces (P.I. A. S.B., April, 1874), lat. 22° 20'. Subsequently 

 I found it in Sambalpur, which is the most eastern district of 

 the Central Provinces (lat. 21° 30'). But the former does not 

 even give its extreme northern limit as it has been found in the 

 Kurrucpur hills of the Monghyr district (lat. 25°). 

 Myiophonus I/orsfieldi I first shot in Sirguja — a native state m 

 I Western Bengal (lat. 23°). Afterwards in the Sutpurus, where 

 it occurred with Tupaia as above, and finally I obtained it also 

 in Sambalpur, where it was found at elevations under 1,000 feet 

 above the sea. Still further north it has been obtained at Mount 

 Aboo ("Stray Feathers," vol. iii. p. 469), lat. 25". 



Myiophonus is, it is true, included in Mr. Wallace's list of j 

 Oriental genera in Central India, but its special employment as 

 a characteristic form of the Ceylon sub-region seems scarcely ^ 

 compatible with a knowledge of its now ascertained wide range 

 through continental India. ; 



During the ensuing field season I expect to be engaged in the 

 geological examination of one of the wildest and least known 

 parts of India — the area between the Godaveri and Mahanudi 

 Rivers. I have great hopes of discovering there further facts , 

 regarding the range of species whose limits are now only imper- 

 fectly known. In the meantime I may state that during the I 



present year I have shot Ilurpactes fasciatus in Sambalpur, thus 

 confirming the late Col. Tukell's statement of its occurrence in 

 the same general tract of country. The above allusion to Tupaia 

 leads me on to record here that I have met with two other species 

 of the genus. 



During an ornithological tour which was made in 1873 by a 

 party of which I was a member— through the islands of the 

 Andaman and Nicobar grouDS— we obtained a species of Tupaia 

 on the Island of Preparis. Our specimen appears to be identical 

 with T. Pegiuensis, which occurs from Pegu to Sikkim. On the 

 Great Nicobar we shot a specimen of the species described in the 

 Novara account as Nicobirienm, and considered then to be 

 worthy of generic distinction. 



In Preparis, it may be added, we also shot a small grey 

 squirrel which is allied to if not identical with S. Assamenns. 

 These, with a monkey {M. catbonariusf), pigs, and probably rats 

 and bats, constituted so far as we could ascertain the mammal 

 fauna of the island. 



Preparis I should perhaps explain is the most northern of the 

 Andaman group lying between Cape Negrais and the Cocos. 



Mr. Wallace has I observe included the Nicobar Islands in 

 the Malayan sub-region and the Andamans in the Indo-Chinese. 

 This separation of the two groups is, I believe, fully justified by 

 the facts. 



Some years ago when working at the avifauna of these islands 

 (J.A.S.B., 1872, p. 274), while recognising the fact of a number 

 of species being common to both groups, I could not resist a 

 conviction as to the existence of a strong Malayan .stamp upon 

 the birds which are peculiar to the Nicobars. 



In conclusion Mr. Wallace's magnificent work needs no praise 

 from me ; but as a field worker and observer I may perhaps 

 venture here to offer my thanks for the valuable mine of infor- 

 mation which it affords. V. Ball, 



Calcutta, September 28 Geological Survey of India 



European Polygalas 



In view of a monograph of the order Polygalaceas which I 

 have in preparation, may I make use of your columns to say that 

 I should be greatly obliged to any correspondents who can send 

 me specimens of any of the less common European Polygalas, 

 especially P. exilis, monspeliaca, microphylla, saxatilis, Preslii, 

 nicceensis, Jlavescens, rosea, sibirica, supina, venulosa, anatolica, 

 or any well-marked varieties. I shall be glad to offer in exchange 

 specimens of some of the rarer British plants. 



6, Park Village, East, Regent's Alfred W. Bennett 



Park, London, October 28 



The Solidity of the Earth 



In his opening address to the Mathematical and Physical 

 Section of the British Association, Sir William Thomson 

 affirmed "with almost perfect certainty, that, whatever may be 

 the relative densities of rock, solid and melted, or at about the 

 temperature of liquefaction, it ii, I think, quite certain that cold 

 solid rock is denser than hot melted rock ; and no possible degree 

 of rigidity in the crust could prevent it from breaking in pieces 

 and sinking wholly below the liquid lava," and that " this pro- 

 cess must go on until the sunk portions of the crust build up 

 from the bottom a sufficiently close-ribbed skeleton or frame, to 

 allow fresh incrustations to remain bridging across the now small 

 areas of lava, pools, or lakes " (Nature, vol. xiv. p. 429). 



This would doubtless be the case if the material of the earth 

 were chemically homogeneous or of equal specific gravity 

 throughout, and if it were chemically inert in reference to it* 

 superficial or atmospheric surroundings. But such is not the case. 

 All we know of the earth shows that it is composed of materials 

 of varying specific gravities, and that the range of this variation 

 exceeds that which is due to the difference between the theoreti- 

 cal internal heat of the earth and its actual surface temperature. 



We know by direct experiment that these materials, when 

 fused together, arrange themselves according to their specific 

 gravities, with the slight modification due to their mutual diffusi- 

 bilities. If we take a mixture of the solid elements of which the 

 earih, so far as we know it, is composed, fuse them, and leave 

 them exposed to atmospheric action, what will occur ? 



The heavy metals will sink, the heaviest to the bottom, the 

 lighter metals (i.e. those we call the metals of the earths, because 

 they form the basis of the earth's crust) will rise along with 

 the silicon, &c., to the surface ; these and the silicon will oxidise 

 and combine, forming silicates, and with a sufBcient supply of 



