Dr. C. A. Ii((isiii — Geologij of Peri ni laJaiuL 209 



are almost identical with the lavas below, except that they are more 

 vesicular. In the quarry above the pumiceous tuff (Fig. 1) one 

 block from the surface deposit is a very similar blackish basalt full of 

 rounded vesicles. Not far from this spot were two loose specimens, 

 a pipy scoriaceous basalt, and a bright red fine-grained tuff containing 

 thin streaks of black glass with small spherulites. The latter 

 rock consists of microscopic yellow-rimmed pieces of brown glass, 

 minutely vesicular, or partly devitrified, even slightly spherulitic, 

 with broken crystals of green augite and of felspar. 



Other surface blocks from north of the harbour and east of the 

 island are basalts or allied rocks, (a) One block (projecting from 

 a coral or limestone conglomerate) has, especially on a weathered 

 surface, the granular appearance of a rock with incipient spherulites. 

 The microscope slice, however, is uniform, except for small slightly 

 paler patches.^ It consists of abundant glass containing minute fel- 

 spars, and is probably a rather basic andesite. [h) Two blocks from 

 farther north contain a few vesicles, are almost a microcrystalline 

 basalt with very little glassy base, both semi-ophitic. (c) A block 

 from north of the harbour resembles the red lava from the adjacent 

 cliff, but is a brighter colour and more vesicular. Others near consist 

 of a black basalt with a few vesicles, (d) Various blocks further east 

 are generally blackish, often compact, and of similar character.- 



Thus the specimens from surface blocks are almost all basaltic, 

 often vesicular aud scoriaceous. They show at each locality 

 a general resemblance petrologically to lavas occurring thei'e in situ, 

 where specimens of these have been obtained. Moreover, in the cliff 

 section north-east of Balfe Point, we seem able to trace a gradual 

 destruction of the underlying lavas through apparently brecciated 

 layers to the surface deposit. Thus the surface blocks found 

 generally over the island at different heights are probably more often 

 disintegrated lava^ than ejected fragments. In either case the 

 blocks might have fallen into a sea where coral sand was accumulating, 

 so that they would become imbedded in calcareous material. The 

 low plains or raised beaches along the coast are frequently formed 

 of a Eecent limestone rich in large corals, Lamellibranchs, etc. I am 

 indebted to Mr. Coomara Swamy for the loan of specimens from this 

 rock, and also for a photograph representing the slope from which 

 blocks of basalt, etc., might fall, to become imbedded in the limestone 

 forming at the base. Even at higher levels, the calcareous material 

 may sometimes represent sediment, often coral sand or mud, deposited 

 during the gradual elevation of the island. The sea being shallow, 



' I have found iu other basalts or basic andesites (as in one from Auvergne) this 

 appearance of incipient spherulites, which are not distinguishable on microscopic 

 examination. 



- Two slices lent me by Mr. Coomara Swamy, taken from blocks near here, are 

 from very similar rock, but with the glassy base better defined and without the brown 

 pyroxene. 



* The disintegration of the rocks may have been helped by a rainfall greater in its 

 amount in past times ; and Mr. .Jones remarks on the tanks built to hold water, now 

 standing empty. 



BECADE IV. VOL. IX. — XO. V. H 



