26 :UK. G. M. DAVIES OX THE [vol. IxXV, 



Fragments under the microscope appear opaque white in air. 

 In a suitable medium, such as cedar oil, they rapidly become clear 

 .and colourless as the liquid penetrates and drives the air out of the 

 pores. The major air-cavities have the form of anastomosing 

 canals. 7 to 10 microns wide. When slightly iron-stained these 

 canals are readily seen, even when filled with Canada balsam or 

 •a similar medium. 



The material is quite isotropic and free from strain-shadows, 

 before and after ignition. Its refractive index is very near 1/552 

 (nitrotoluol), well above 1--542 (oil of cloves), and under 1-5(30 

 (dime thy laniline). Thin sections in Canada balsam show a re- 

 fractive index under y quartz and apparently very near a quartz. 

 After ignition the value falls to about 1*542 or even lower. Allo- 

 phane has a refractive index of TI9 (Miers). The hardness is not 

 quite 2. and the specific gravity is 244, against 1*85 to 1*89 for 

 ailophane (Dana). This was found by floating fragments in dilute 

 bromoform. and determining the density of the liquid by the 

 TVestphal balance. The specific gravity after ignition is 216 or 

 2-17. 



Xo other minerals appear to have been formed with the halloy- 

 site. W Tien the material and its enclosed and adhering sand-grains 

 were washed and panned, only heavy minerals of the kinds common 

 in the sand were seen : namely, ilmenite, limonite, zircon, tourma- 

 line, staurolite, rutile, kyanite. yellow anatase, and magnetite. 



Mr. A. Broughton Edge has made a chemical analysis of this 

 material. The sample examined was very carefully selected by 

 him from material obtained by Dr. J. W. Evans, and the powdered 

 substance was pure white and free from visible iron-stains and sand- 

 grains. His results are set forth in columns I & II below, while 

 analyses of halloysite and allophane are given for comparison in 

 columns III <£ IV respectively : — 



I. IT. III. IT. 



Si0 2 41-88 0-6980 42-6 19-58 



Al o 3 36-26 0-3555 36'4 37-30 



Fe*P 3 0-30 ... ... 0-11 (FeO) 



MgO none 



€aO 0-23 0-0041 ... 1-36 



2sa 2 trace 



K o trace 



HoO. atl00°C 7-71 ... 7'8 20-76 



H~O.100°C.to250 c C. 0-85 



H.,0, ignition 13-06 0-7255 13'2 18-43 



C0 2 0-17 0-0038 ... 2-44 



Totals 100-46 100-0 99'98 



I. Halloysite. Worms Heath. Analyst, A. B. Edge. 

 II. Molecular proportions corresponding to I. 

 HI. Halloysite. Angleur (Belgium). Analyst. H. Le Chatelier. Bull. 

 Soc. Franc-. Mineral, vol. x (1887) p. 210. Recalculated to include 

 hygroscopic water. 

 IT. Allophane, Charlton (Kent). Analyst, A. B. Xorthcote. Phil. Mag. 

 ser. 4, vol. xiii (1857) p. 341. 



