H 



242 



NATURE 



{July 10, 1879 



The Malabars, who were introduced into Mauritius as Coolies, 

 would not sleep under tamarind trees, on account of their 

 supposed noxious effects ; but it is possible that superstition has 

 something to do with their objection. 



*" ■ S. P. Oliver 



On the Origin of Certain Granitoid Rocks 



Dr. Callaway's interesting letter with the above heading in 

 Nature (vol. xx. p. 219) tempts me to send you the following 

 paragraph from my paper in the Quart. Jourti. Geolog. Soc. for 

 May, p. 286, -in which the halleflintas of the Arvonian there 

 mentioned are first described : — 



"The mode of behaviour of the quartz also here is particu- 

 larly interesting and instructive in regard to the changes which 

 many crystalUne rocks have undergone, especially the gneisses. 

 In some cases the quartz is seen in distinct fragments, but yet 

 coalescing, as if attracted together by some natural affinity from 

 the surrounding material. In the next place the grains are so 

 compressed together (and yet distinctly fragmentary) that all 

 other material is removed, and nests of pure quartz grains only 

 are seen, having a very ciystalline appearance. By this selective 

 process also the darker material is brought together and made to 

 fold round the nests, so that a banded or imperfect flow-structure 

 is given to the rock. AU this looks as if an incipient gneiss was 

 being formed, the metamorphic action being incomplete, a kind 

 of semi-metamorphism and softening having taken place suf- 

 ficient only to allow the particles to arrange themselves accord- 

 ing to their natural affinities." 



It will be seen that the conclusions arrived at by Dr. Callaway 

 in his recent examinations of similar rocks in Shropshire are 

 almost identical with those previously formed by myself in Pem- 

 brokeshire. The careful microscopical examination of rocks of 

 an intermediate type like these halleflintas appear to be, cannot 

 fail, 1 think, to clear up some of the difficulties hitherto expe- 

 rienced in endeavouring to explain the origin of many of the 

 crystalline rocks. HENRY HiCKS 



Hendon, July 4 



Distribution of the Black Rat (Mus rattus, Linn.) 

 in Italy 



It may interest the readers of Nature to know that the 

 black rat is very abundant and widely distributed in Italy and 

 her islands. In the Central Collection of Italian Vertebrata which 

 I have founded in the Florence Zoological Museum, I have a 

 large series of specimens from no less than fifteen localities, viz., 

 Domodossola, Casale, Florence, Radda, Arezzo, Castelfalfi, 

 Lecce on the continent, Bastia (Corsica), Cagliari (Sardinia), 

 Castelbuono Madonie (Sicily), and from the islands of Elba, 

 Pianosa, Montecristo, Giglio, and Lipari. On the smaller 

 islands the larger M. decumanus does not exist at all, but else- 

 where the t«o species live side by side. In the Florence 

 Museum we have M. decumanus in the cellars, and M. railus 

 upstairs. This proves that the black rat is very far indeed from 

 extinction with us ; I should say that it is generally more 

 abundant in Italy than its larger congener, at least such is my 

 experience. I 



I may add that we have tivo, if not three, very distinct 

 varieties of M. rattus, viz., the typical Mack M. rattus, the 

 grey and white M. tectorutn, Savi, and the brown hirsute 

 M. alexandrinus. The two former are positively one species, 

 and I have Ihem from the same litter ; the latter is, I believe, 

 generally admitted to be specifically identical with M. rattus. 



Henry H. Giglioli 



Royal Zoological Museum, Florence, July 4 



towards the free end of the spine. So far as I am aware, this 

 structure is unique amongst the brachiopods. Mr. Davidson has 

 kindly undertaken to note this interesting fact in the explanation 

 of the plates of his forthcoming monograph, the text having been 

 printed off before this observation was made ; but I should like 

 to draw the attention of palaeontologists to the point, as perhaps 

 similar structures may be found in other brachiopods. The ma- 

 terials are in Mr. Davidson's hands for extended notice when his 

 leisure allows him. John Young 



Hunterian Museum, Glasgow University, June 



Barbed Hooklets on Spines of a Brackiopod 



Mr. Thomas Davidson, F.R.S., describes, on p. 275, and 

 figures, in pi. xxxiv. of the Supplement to his " Carboniferous 

 Brachiopoda," now on the eve of publication, some important 

 points in the structure of Spinfa-a lineata, Martin, which speci- 

 mens in my collection have revealed. In this species the shell 

 structure is minutely punctate, and the flattened spines, which 

 are usually broken^ off short, contain in their interior a double 

 canal, that terminates upon the outer surface of the shell in a 

 series of double pores. I have recently been fortunate enough to 

 find a specimen from the High Blantyre limestone shales having 

 the spines in place. It appears that these spines are provided 

 with numerous marginal opposite hooklets usually pointing 



The Serpent Mound of Lochnell, near Oban 



I WALKED over yesterday from here to examine this for 

 myself. I started with some feelings of doubt as to whether it was 

 not one of those fantastic shapes naturally assumed by igneous 

 rocks, seen through the spectacles of an antiquarian enthusiast. 

 I came away quite satisfied that it is an artificial shape, 

 designedly given, and deliberately intended to represent a snake. 

 It partly closes the entrance of a singular little rock amphi- 

 theatre with a waterfall at the head (the north end of it), the 

 Loch being to the southward. There is a raised plateau to the 

 northward of the serpent, nearly square. The ground is 

 apparently a rubble"of gravel, stones, and dirt, such as is found 

 in moraines. The head of the snake had been opened, and 

 showed a quantity of stones ^with some indication of a square 

 chamber in the middle. 



I do not pretend to any antiquarian knowledge. The impres- 

 sion that it suggested to me, on the spot, was that a party had 

 endeavoured to entrench itself, at the spot, but had been 

 attacked before the entrenchment was complete on more than 

 one face, and that the rampart was then converted into the 

 snake form to commemorate either a successful assault, or the 

 successful defence of an unfinished work. 



ilan, of 



EUvaUorv 



I inclose you a sketch plan and elevation, of a very rough kind, 

 w hich I made on the spot and have not retouched since, except 

 by inking over my pencil maiks. 



Vou have already (fome years back), given a drawing and 

 description of it. It should be stated that it is at the north-west 

 corner of Lochnell, close alongside of the road from Oban to 

 CaUanach. C. W. M. 



Oban, June 19 



The Origin of Hail 



I SHOULD feel much obliged if any of your readers would 

 kindly explain for me the following "explanation" of the origin 

 oiJiail; which I have come across while reading for an examina- 

 tion : — 



"Hail. — It consists of concentric layers of ice, and is caused 

 by electricity. Imagine two clouds, A and B, charged with dif- 

 ferent fluids, and suppose that a drop of water falls from A. 



Its 



