BY A. N. LEWIS. M.C , LL I!. J7 



Mt. Wedge, on the sides of Mt. Mueller and the exposed 

 summit of Mt. Bowes, indeed of all the rocks of this series 

 in the locality, points to the conclusion that these must all 

 have once formed the top of a plain. Farther south and 

 west the peaks of the Arthur and Frankland Ranges consist- 

 ing of the old Pre-Cambrian schists have a remarkable 

 accordance in altitude, suggestive of an ancient peneplain, 

 but whether of the same or an earlier cycle of erosion is a 

 problem for the future. There is no evidence at pi'esent 

 upon which to fix the date of the peneplanation of the 

 Cambro-Ordovician rocks of the area, but it was certainly 

 earlier than the Permo-Carboniferous glaciation. 



The diabase intrusions raised the sediments that had 

 been deposited from the western lands in the coastal seas 

 of Jurassic times and earlier and instituted our present 

 cycle of erosion, but the extent to which the land to the west 

 was affected by these intrusions or earlier and later earth 

 movements and whether the older rocks of the West Coast 

 were ever covered by the Trias-Jura sediments is not yet 

 known. The diabase, however, certainly did force its way 

 through the older quartzites in places, as at Mt. Anne. 



The direction of the present drainage was probably 

 determined by the landscape immediately after the diabase 

 intrusions, during the Upper (?) Cretaceous. The rivers 

 are therefore here, as throughout Tasmania, subsequent 

 streams. The fact that the diabase with incumbent sedi- 

 ments rose to a height of 4,000-6,000 feet above present sea 

 level, while the top of the older rock to the west now does 

 not exceed 3,000 feet, yet the rivers run from west to east 

 cutting, from the comparatively low lands of the west, in 

 huge, steep sided valleys and gorges through the mountain 

 systems that now stand highest, indicates that in Cretaceous 

 times the mountains to the west stood, or were covered with 

 other rock, since removed, which stood, twice as high as they 

 now are to be seen — e.g., the Huon could reach the sea from 

 its point of origin by several channels that do not rise over 

 1,000 feet, but it appears to cut through a ridge between 

 Mt. Weld and Mt. Picton, 3,000 feet higher. It thus provides 

 a good example of a subsequent stream being kept in its 

 course by its original channel, formed in very different 

 strata (in this case probably Trias-Jura sandstones) from 

 those lying below, which now stand out as mountains of 

 circumerosion. 



The Huon, Weld, and Serpentine Rivers are on the 

 verge of maturity although their tributaries are, as usual 



