454 THE GEOLOGY OF TilK NKW HEBltlDKS, 



natiu'e of the finest dust, the particles never exceeding 0*02 mm. 

 diam.; the fragments in the coarser bands average 08 mm. 

 diameter. Fragments of volcanic glass and pumice, and in small 

 quantities felspar granules, are invariable constituents; accessories 

 are particles of magnetite and pyroxene, and organic remains, 

 chiefly tests of small foraminifera. 



One variety noted in the series differs rather widely from the 

 type-speqimens, and deserves special mention. It outcrops as a 

 compact band a few feet in thickness at the 300 ft. level in the 

 gorge of the Ai Stream. It is quite hard and much coarser in 

 texture than usual. Felspar referable to andesine constitutes 

 about 8 % of the rock and is present as fragments sometimes 

 1-5 mm. diam.; about another 1 % is represented by augite and 

 magnetite in very small grains; the rest of the section consists of 

 irregular particles of fibrous volcanic glass and 2-)umice fragments 

 much infiltrated by calcium carbonate, and attaining a maximum 

 length of 1-5 mm. 



Professor Liversidge has recorded the analysis of a specimen 

 of a rock collected at Havannah Harbour, from a terrace at an 

 elevation of 525 ft. The rock is described as greyish- white in 

 colour and readily friable. This can be no other than the Efate 

 soapstone.* 



ii. Raised Reef Limestone. — This limestone is built 

 up of the fossil remains of calcareous reef-haunting forms of 

 life, amongst which the corals figure conspicuously. In most 

 instances it is so recent that the cell-cavities have not yet been 

 filled up, nor has the intimate structure been lost. Tracing the 

 reefs back from newer to older, the limestone becomes noticeably 

 more compact with obliteration of cell-spaces and development 

 of crystalline calcite. No true dolomites were obser\'ed. 



Often a more darkly coloured layer resembling dense travertine 

 appears as a facing half an inch or more in thickness; this seems 

 to have resulted from concentration of the more insoluble parts 

 of the limestone by percolating water. 



* Journ. Proc. R. Soc. N. 8. Wales, xiv. 161 [1881]. 



