254 The Tripolite Deposits of Lilicur. 



every point of the compass. The general uniformity in the 

 texture and colour of the deposit is broken here and there 

 by dark-stained, sharply -defined bands and veins, the origin 

 of which is due to desiccation and subsequent infiltration 

 from above. Where the desiccation cracks were of sufficient 

 width (from 1 to 2 inches) they have been filled by a 

 brownish black clay, and then stand out in harsh contrast to 

 the downy clearness of the surrounding silica. In other 

 places the contracting mass has been rent by mere capillary 

 joints, along which percolating waters have caused a partial 

 solution of the silica, and its ultimate resolidification into a 

 colloid form. This process is still going on, and the result 

 is an occasional band or recticular patch of opal of a waxy 

 lustre and pale yellow colour. The specific gravity of the 

 pure tripolite is 1-908, that of the opal 2-008.* 



It has been already suggested that this and similar lakes 

 had no inlet, properly so-called, but that its contents were 

 derived from the meteoric waters falling within its own 

 narrow drainage area. Had any extraneous organic substance 

 been carried into the pool, and there commingled with the 

 diatoms, traces in the form of carbonaceous or bituminous 

 matter must have remained, and would now be easily 

 recognisable in the white silicious stratum. In the absence 

 of any such traces, it must be inferred that there was an 

 overflow channel through which any floating matter was 

 removed. In reality there was such an outlet, for along the 

 existing gully, which runs past the southern edge of the 

 deposit into the Caralulup Creek, cake-like patches of 

 tripolite can be traced under the turf nearly the whole 

 distance to the valley of the main stream below. 



About three-quarters of a mile to the east of M'Kenzie's 

 mine there are two shafts, not now accessible, but respecting 

 which the following information has been supplied by Mr. 

 Murray, who sank them: — The southern shaft went through 

 a layer of tripolite 2 feet thick, and of similar appearance 

 to that found at M'Kenzie's, after sinking through 40 feet of 

 claydrift< The second shaft, which lies a few chains north 

 of the former, is 75 feet deep, pierced two layers of basalt, 

 and beneath them a bed of tripolite 18 inches thick. 



Immediately to the north-west of the village of Lilicur, 

 and close to the western edge of a basaltic outlier, fragments 



As determined at the School of Mines laboratory. 



