ROCK SPECIMENS COOKSEY. 77 



Pumice Pebbles. Pebbles of pumice stone, the largest of which 

 resemble a walnut in size, all much water worn and rounded, 

 were collected from various places on the outer circumference of 

 the Atoll, and possibly occur on all of these islets. They possess 

 a fibrous texture, and contain macroscopic crystals of sanidine. 

 The colour varies from light to dark grey, one or two having a 

 brown or greenish tinge. Similar pebbles occur on most of these 

 Pacific Islands,* and along the eastern coast of Australia.! 



An analysis of one which was much rounded by attrition, and 

 possessed a very light grey colour, gave the following percentage 

 composition : 



Hygroscopic moisture ... -09 



Loss on ignition 2-29 



SiO 2 66-50 



Fe 2 O 3 3-21 



Al a 3 16-84 



CaO 3-03 



MgO 1-03 



K 2 5-44 



Na 3 O 2-53 



P 2 O 5 trace 



100-96 



A partial analysis of another pebble of a darker shade gave 

 60-37 % of Si0 2 . 



On referring to analyses already published of drift pumice, 

 the figures above are seen to agree very closely with that 

 made by Prof. A. Liversidge, F.R.S., of white pumice found on 

 the beach at Bondi, near Sydney, j and again with some others 

 published somewhat earlier of ashes and pumice derived from the 

 eruption of Krakatoa in 1883. The pebbles examined by Prof. 

 Liversidge were collected before this eruption took place, but he 

 suggests that this volcano may have been the source from which 

 the pebbles were derived. 



It is possible, of course, that the specimen obtained from 

 Funafuti may have found its way from there also, as its analysis 

 would seem to suggest ; but its path would have been so long 

 and devious, that one naturally turns to a nearer and more likely 

 source. An obvious one is that of Tanna, in the New Hebrides. 

 In the same publication, however, Prof. Liversidge gives some 

 analyses of dark or black lava from the latter place, which differ 



* Of. The Solomon Islands, by H. B. Guppy. Nature, Dec. 5, 1878. 

 t Of. Jukes. Voyage of H.M.S. " Fly," 1847, p. 336. 

 t Journ. Roy. Soc. N.S.W., xx., 1886, p. 235. 



