18 Howard Fox — On a Soda Felspar Rock — 



Continuing our progress along the northern side of the headland, 

 we find the greenstone and soda rock much intermixed, and 

 compact blue slate is interbanded with numerous blue limestone 

 bands, from a few inches to several feet in thickness, dipping south, 

 of east. Both slate and limestone occasionally weather in circular 

 holes and contain rusty-coloured material in the same way as the 

 soda rock. 



Dr. Hinde found that a section of the blue limestone from "e" 

 was principally made of echinodermal fragments, probably of 

 crinoids, and there were also portions of Polyzoa like Fenestella. 



At "/" we find this soda rock, for an area of 30 square feet, 

 assuming a gray nodular character. The compact rock passes into 

 one composed of gray nodules from 3 to 10 mm. in diameter, as 

 shown in Fig. 4. The nodules at the outer edge of one portion 

 of this rock show spherulitic structure. The spherulites are crowded 

 together, and occasionally attain a diameter of 10 mm. Thin veins 

 of quartz traverse the nodules, which often weather gray, in cup- 

 shaped prominences. In other cases they weather white, and the 

 polygonal sutures, filled with ferruginous matter, give the rock 

 a scale-like or mosaic appearance. 



tp^*^ 



Fig. 4. Sketch (natural size) of gray nodular soda rock with spherulitic structure, 

 from the jSTorthern Cliil of Dinas Head. 



Mr. Teall examined three sections of this rock, and reported as 

 follows : — 



"No. 353. A remarkable spherulitic rock. Spherules sometimes 

 measuring ^ inch in diameter. 



The central portions of the spherules are generally composed of 

 crypto-crystalline material. The outer portions of radiating blades 

 or prisms of felspar, presumably albite. Ferric oxide, probably 

 resulting from the decomposition of a ferriferous carbonate, is 

 scattered through the slide in irregular patches, and concentrated in 



