at Dinas Head, North Cornwall. 



19 



veins. Some of the patches by their form suggest that the ferric 

 oxide is a pseudomorph after a carbonate. 



The interference of adjacent spherulites produce polygonal sutures, 

 in which the ferric oxide is sometimes concentrated ; but it occurs 

 also in the spherulites. 



No. 354. Similar to the last. Ferric oxide in radial streaks 

 between the blades or prisms of felspar which form the radial 

 portions of the spherulites. 



No. 355. Similar to above, but with the ferric oxide almost 

 wholly concentrated in the polygonal sutures formed by the mutual 

 interference of adjacent spherulites." 



As the microscope failed to disclose the composition of this rock, 

 I sent specimens of the three chief varieties to Mr. J. J. Beringer, 

 F.C.S., of Camborne, who kindly consented to analyse them. He 

 entrusted much of the work to his pupil, Mr. Arthur F. Hosking, 

 and sent me the following results : — 



I. Specimen was the light brownish chert-like variety, weathering 

 white, with cavities filled with rusty-brown material from "c" in map. 



II. Specimen was the dark bluish-gray compact variety, weather- 

 ing white, from " 6 " in map. 



III. Specimen was the gray nodular variety from "/" in map. 



Loss on ignit: 

 Silica 



Titanic acid 

 Alumina . . . 

 Ferric oxide 

 Lime 

 Magnesia 

 Alkalies ... 



III. 



1-6 



64-6 



1-2 



20-4 



0-7 



1-3 



0-1 



10-1 



Mr. Beringer adds : " The silica in HI. was not directly de- 

 termined. The alkali is mainly soda; by trituration with acid it 

 represented 9 "6 per cent, of soda, on the assumption that soda was 

 the only alkali present. In I. and HI. the bulk of the iron and 

 lime is in a form easily soluble in acids ; this is partly true of II., 

 but the soluble fraction is very smalL" 



In a subsequent communication Mr. Beringer informed me that 

 the potash in one of these specimens was 0-47 per cent. 



I am indebted to Mr. J. Hort Player, F.C.S., of London, for the 

 following analysis of the compact light-brown chert-like rock from 

 ** c," free from weathered crust or nodules. 

 Dinas Head Eock. 

 Silica 

 Titanic acid 



Alumina... . 

 Ferric oxide . 

 Ferrous oxide 

 Magnesia 

 Lime ... , 

 Soda ... . 

 Potash ... . 

 Loss by ignition 



66 



19 



April 28, 1894. 



100-1 

 J. HoKT Player. 



