Ridley — Raised Reefs of Fernando de Novonha. -±07 



in the guano of Ilha Rapta. In fact in many places one can 

 easily trace the reef rock into these so-called seolian sandstone. 



Mr. Branner (1. c. April, 1890, p. 249) gives the analysis of a 

 piece of this rock which contains 92*27 per cent, of carbonate 

 of lime, and only 2*20 p. c. silica. Again, on page 256, he 

 gives two analyses, one of a piece of sandstone from Ilha 

 Rapta, a clean and compact piece of one of the "tall jagged 

 points left by the etching out of the surface by the combined 

 action of rain water and ocean spray." This which would 

 naturally have lost more of its soluble calcium carbonate than 

 silica gives 98*33 per cent, calcium carbonate and *09 per cent 

 of silica and other matter insoluble in concentrated nitric 

 acid ! Can one call this sandstone at all ? 



I may here mention I have just returned from a short visit 

 to Christmas island in the South Atlantic ; an oceanic island, 

 south of Java and in many points recalling Fernando de 

 Xoronha. It has a high ridge rising very straight out of very 

 deep water, I am told there is a volcanic backbone to the 

 island, and I found pebbles of tuffs and traps on the shore, but 

 had no time to reach it. There are no sandy bays or dunes as 

 in Fernando de Noronha. Here and there a little bay a few 

 yards across has coral sand in it ; but the whole of the island 

 is covered with rock exactly like that of Ilha Rapta. Here 

 and there are cliffs, layer over layer laid straight down, of this 

 rock, just as at Fernando de Noronha. What force could 

 hare hurled sand dunes from an abysmal depth to the top of 

 the lofty hill of Christmas island and where did the sand come 

 from ? Comminuted shells, coral dust, etc., form the softer 

 bottom in many of these places, but sand is not plentiful, if it 

 occurs at all. 



But there are true seolian sandstones in Fernando de No- 

 ronha, on Sao Jose we found a block of real sandstone ; nearly 

 pure silica, apparently made of drift sand and very hard and 

 compact. It contained a pseudomorph of a large crystal of 

 feldspar in quartz and two or three shells (marine) well pre- 

 served. We were a little doubtful as to the position of this 

 rock, as it was in the fort and might have been imported. 

 But at Bahia San Antonio there were large sand dunes and 

 seolian sandstone forming. In most spots it was feebly held 

 together, in some more compact. The sand was being aggluti- 

 nated by carbonate of lime, true, but whence was this carbo- 

 nate of lime ? of corals, nullipores, sea-shells ? Certainly not. 

 It was derived from innumerable shells of Helices and Bulimi. 

 There was, except a stray shell here and there dropped by a 

 sea bird, not a marine organism, giving up its carbonate of 

 lime to form the sandstone. This true aeolian sandstone was 



Am. Jour. Sci.— Third Series, Yol. XLI, No. 245.— Mat, 1891. 

 27 



