138 Correspondence — W. A. E. Uss/ier — A. B. Hunt. 



EADIOLARIAN ROCKS OF THE CULM MEASURES, DEVONSHIRE. 



Sir, — I wish to call attention to the unfortunate mistake which 

 I have made on pp. 4, 105, 106, 107, 108, and 109 of the Geological 

 Survey Memoir on Plymouth and Liskeard, 1907, in attributing to 

 Mr. Fox alone various statements which I have quoted from the 

 joint papers of Messrs. Hinde and Fox on the Radiolarian rocks of 

 the Culm Measures, in the Quart. Journ. Geol. Soc, vol. li, 1895, 

 and in the Transactions of the Devonshire Association, vol. xxviii, 

 1896, and in Proc. Geologists' Association, vol. xx, pp. 88, 92, 1907. 

 I desire to express my regret, and to offer my apologies to these 

 authors for the unintentionally deficient references to their joint 

 papers. W. A. E. TJsshek. 



28, Jermyn Street, S.W. 

 February/ Uth, 1908. 



THE LIQUID AND PNEUMATOLYTIC THEORIES OF GRANITIC 



MINERALS. 



SiK, — I have noticed with much regret that the conclusions arrived 

 at by the Geological Survey ^ as to the crystallisation of the West 

 Country Granites are in hopeless conflict with several communications 

 which the Geological Magazine has honoured me by publishing. 



Broadly speaking, the Survey authorities have adopted the high 

 temperature gaseous theory,'' whereas I have assumed the impregna- 

 bility of the low-temperature liquid theory. Any attempt at 

 reconciliation is useless, but it may be as well if I submit the list of 

 the authorities on which I have relied. They are in order of date as 

 follows : — 



(1) Sorby, " Microscopical Structure of Crystals " : Q.J.G.S., 1858. 



(2) Sorby & Butler, " Rubies, Sapphires, and Diamonds " : Proc. R.S., 1869. 



(3) Hartley, " The Identification of Liquid Carbonic Acid in Mineral Cavities " : 



Royal Micro. Soc, March 1st, 1876. 



(4) Sorby, "On the Critical Point in the Consolidation of Granitic Rocks"; 



Mineralogical Mag., September 6th, 1876. 



(5) Hartley, " On Variations in the Critical Point of Carbon Dioxide in 



Minerals," etc. : Journ. Chem. Soc, September, 1876. 



(6) Hartley, " Observations on Fluid Cavities " : Journ. Chem. Soc, 



March, 1877. 



(7) Hartley, "Attraction and Repulsion of Bubbles by Heat" : Proc. R.S., 1877. 



(8) Hartley, "On the Constant Vibration of Minute Bubbles": Proc. R.S., 1877. 



(9) Report on the Conditions under which Liquid Carbonic Acid exists in Rocks 



and Minerals, by a Committee consisting of Walter Noel Hartley, 

 F.R.S.E., E. J. Mills, D.Sc, F.R.S., and W. Chandler Roberts,, F.R.S. 

 Drawn up by W. N. Hartley, F.ll.S.E. : Rep. Brit. Assoc, 1877. 



(10) A. Daubree, "E'tudes Syuthetiques de Geologie Experimentale " : 1879. 



(11) Sorby: Address to the Geological Section of the British Association, 1880. 



(12) Fouque et Levy, " Synthcse des Miueraux et des Roches " : 1883. 



I am bound to admit that the first chapter of Daubree's " Experi- 

 mental Geology " justifies the views of the Geological Surveyors, and 



1 "Land's.End District," pp. 49-60, 1907. 



- " ' Pneumatolysis ' refers to the action of gases above critical temperature" 

 (" Falmouth and Camborne," p. 168, 1906). 



