president's address — SECTION c. 155 



111 1861 tlie late Mr. F. T. Gregory gives in his paper, " On the 

 Geology of a Part of Western Australia," an account of this lateritic 

 deposit capping the Darling Range, and claims for it a Devonian Age. 

 This observer mentions the important fact that the deposit blends 

 gradually with the upper surface of the granite, and states that it would 

 seem to owe its origin to the decomposition of the granite in situ. 



The Rev. W. B. Clarke, in his " Sedimentary Formations of New 

 South Wales," remarks : — " Mr. T. F. Gregory indicated on his map, and 

 in his report, the existence of Devonian rocks near York, and in other 

 parts of that colony. Having examined the rocks so indicated, I can 

 only state my belief that they have no pretension to any such antiquity, 

 and are probably mere collections of loose granitic matter, and other 

 drift cemented by ferruginous paste, which has since become trans- 

 mitted into concretionary nodules and hematite. There are also 

 pebbles of trap, much decomposed, in the so-called Devonian. They 

 mav be, perhaps, more properly considered as representing the laterite 

 of India." 



It is on these historical grounds that laterite has been adopted in 

 Western Australia as the name for these residual deposits, rather than 

 the term " Saprolite," which American writers have suggested. 



The various reports of the Geological Survey contain numerous 

 descriptions of these lateritic deposits, and are often accompanied by 

 analysis. These analyses show variations in alumina from 7.52 to 

 44.66 per cent. ; ferric oxide, 10.02 to 88.23 per cent. ; silica, 1.53 to 

 23.26 per cent. ; combined water, 8.10 to 26.44 per cent. ; and oxide 

 of titanium, .59 to 3.10 per cent. 



A recent analysis of a ferruginous laterite from Comet Vale 

 (North Coolgardie) is of interest, " on account of the high percentage 

 of chromium, mostly in the form of a hydrate readily soluble in hydro- 

 chloric acid, the balance being present in the form of chromite." The 

 analysis gave 79.01 per cent, of ferric oxide, 5.30 per cent, of chromic 

 oxide, 3.14 per cent, of silica, and of water 12.35 per cent. Some of 

 the laterites have proved to be more than appreciably auriferous. 



In the southern portion of the State, where the rainfall is greatest, 

 the lateritic deposits support an abundant vegetation, the well- 

 known karri and jarrah growing in all their splendor thereon. In 

 fact, the mapping of the lateritic deposits of this portion of the State 

 would define the areas over which both karri and jarrah occur. 



Elsewhere in the State the laterites support but a scanty 

 vegetation. 



So far as our observations have been extended, the laterites, for 

 the reason previously given, occur as disconnected outliers which 

 once formed part of a continuous deposit. It is difficult to escape the 

 conviction that since they were deposited a considerable time may 

 have elapsed, hence the laterites may be of some geological antiquity, 

 of which possibly the thickness and the state of consolidation may be 

 some measure. 



We have, however, as 3'et little authentic evidence on this point, 

 though it may be mentioned that in a bore put down at Coolgardie, on 



