Major- Gen. MacMahon — Nature's Manufacture of Serpentine. 7 1 



their loads of "earth" are gliding up and down the steep hill-side. 

 Apart from its being a source of wealth and industry in the 

 country, this extension at Woburn of the Fuller's-earth works is an 

 interesting item in Bedfordshire geology, and the borings will 

 determine probably the general arrangement of this mineral, 

 regarding which, up to the present time, no particular notice has 

 been taken. 



VJL — The Mantjfactuee of Serpentine in Nature's Laboratort. 



A Reply. 

 By Major-General C. A. MacMahox, F.G.S. 



PEOF. BLAKE, F.G.S., President of the Geologists' Association, 

 has been good enough to send me cuttings from his recently 

 published work " Annals of British Geology " containing his running 

 comments on papers by me published during the period embraced 

 by his volume, and for which I desire to tender him my best thanks. 



I think it will be more courteous on my part to offer a few obser- 

 vations by way of reply to Prof. Blake's criticisms than to allow 

 them to pass in silence ; but I must confine myself to one paper, by 

 way of sample. I select that bearing the title at the head of this 

 communication (published in the Proc. Geol. Assoc, vol. xi. p. 427), 

 as the subject discussed in it is of general interest to geologists. 



The first extract from the Annals of British Geology I select for 

 comment runs as follows : — 



" He then enters into the chemical question, and explains how 

 carbonic acid will decompose silicates of magnesia and iron. The 

 principal mineral altered being olivine, he shows that if from 2 

 molecules of this (MgFe)4 SigOs, one molecule of ferro-magnesian 

 oxide is removed, MgFeO, and two molecules of water added, H4O2, 

 we get Serpentine, H^ (MgFe)3 SigOg, but 'as this involves an 

 increase of volume some silica may also be removed.' This last 

 suggestion will, of course, alter the above, and bring it into harmony 

 with the method suggested by Roth, as quoted by Teall (Brit. 

 Petrography, p. 106), i.e., 5 molecules of olivine=10 MgO+5 SiO.^ 

 - (4 Mg 0+Si OJ+i H^O^e Mg 0,-f4 Si O2+4 H20=2 mole- 

 cules of Serpentine." 



The sentence " as this involves an increase of volume some silica 

 may also be removed " is marked by inverted commas and professes 

 to be a quotation from my paper. Prof. Blake employs inverted 

 commas, apparently, in order to convict me of a blunder out of my 

 own mouth; the word "also" implying that some silica may have 

 been removed from the tioo molecules of (MgFe) O2' Si O2 in addition 

 to the molecule of ferro-magnesian oxide ; and as the loss of this 

 silica is not shown in my account of the tiBO molecules of olivine, 

 my calculation must be wrong. 



Strange to say, the passage quoted under inverted commas does 

 not occur in my paper. Not only did 1 not write the sentence 

 given as a quotation, but it involves a serious misrepresentation of 

 the views expressed in my paper. 



