81 



l^roduct resulting from the decomposition of the neigliliourino 

 granitic and hornblendic rocks. 



Tlie travertine has frequently a concretionary structure, and 

 includes sand and fragments of the adjacent rocks ; sometimes it 

 cements the gravel of the plains to a form of conglomerate. The 

 thickness of the travertine crust varies cousiderahly up to 

 twelve feet. 



The lenticular masses of black travertine attaiii to three or four 

 feet in the longer diameter ; if broken, or the pieces be rubbed 

 together, an empyreumatic odour is given off. Aji analysis of a 

 sample from Ferdinand River gave the following percentage 

 values : — Carbon, 8 : calcic carbonate, 38 ; magnesic carbonate, 

 11; silica and oxide of iron, itc, 4:3. (Similar blackened con- 

 cretionary travertine is described by Professor Tate from the 

 country around the Great Bight in Trans. Roy. Soc. S. Aust., 

 vol. 3, p. 11-5). 



Chalcedony^ as a stratified deposit was found in sitn at several 

 places, especially along the western bank of Ferdinand River, 

 where it forms a stratum of three feet thick beneath travertine. 

 As debris, chalcedony is found in great abundance all over the 

 area under consideration ; not only profusely scattered over the 

 plains, and forirung an integral part of the sands, but abundantly 

 diffused over the granitic rocks of this region. It was found as 

 high as 2,700 feet on Mount Sir Thomas, and also on the top of 

 Mount lUbiUie, 3,100 feet. 



These siliceous accumulations, as well as the above-mentioned 

 calcareous ones, must be regarded as aggregations of siliceous or 

 calcareous material, as tlie case may be, derived from the Tertiary 

 or the fundamental Azoic rocks. Their formation may still be 

 going on, especially in and near ci'eek-beds ; and no doubt whether 

 it be continuous or not, it is contemporaneous with the latest 

 and jnost abundant superficial deposit — that of the sand. 



The sanclridges reach a height of, not exceeding, 60 feet. They 

 have a general trend of north and south, though their course is 

 occasionally interrupted by granitic outcrops. The material is a 

 fine drift-sand, chiefly composed of quartz, either white or 

 ferruginous; particles of felspar are seldom discernible. The 

 thickness of the sand-cover is very variable ; anything Hke a 

 mhsoil could not be seen, unless the wide loamy flats which occur 

 between, and particularly on the south-east side of the ranges, 

 are to be regarded as representing it. 



The loamy flats are generally watered by creeks, and where 

 this is the case flxiviatile gravels are of frecjuent occurrence. Ko 

 gravel-plains, as the term is understood in the northern part of 

 South Australia, exist in this region ; but its gravel-beds are of 

 true fluviatile origin — the outcome of the erosive force of the 



