BY A. N. LEWIS, M.C.. LL.B. 25 



quartzite varies considerably from one locality to another 

 it should be possible to discover whence this mass came, and 

 the light such an investigation would throw on the mechanics 

 of the diabase intrusions would well repay the trouble. 



The diabase adjacent to the quartzite is of a glassy, 

 homogeneous texiure for about 100 feet, in which space it 

 changes to the ordinary coarse-grained crystalline rock 

 common on the mountain tops. This is interesting as show- 

 ing conclusively that coarse crystals in the diabase are not 

 an indication that the rock in question cooled at a great 

 distance below the then surface. This close-grained diabase 

 is sufficiently different in nature to be clearly distinguish- 

 able from the ordinary diabase at a distance of several 

 hundred yards. 



In the centre of the quartzite patch a small cirque has 

 cut into it to a depth of about 75 feet, and in the centre of 

 this depression can be seen a dyke of glassy diabase about 12 

 feet wide penetrating the quartzite. The junction line be- 

 tween the quartzite and the diabase is finely marked, but the 

 former rock show.s no signs of having been affected by the 

 diabase. 



The diabase cap of Mt. Anne has been greatly denuded 

 by glacial action and has nearly disappeared. On the sides 

 of the cirques thot eat right into the heart of the mountain 

 the junction between the diabase and the country rock it 

 overlies can be clearly distinguished. There is probably 

 no place in Tasmania in which the diabase intrusions can 

 be studied with greater prospects of good results. 



(e) Post-Diabase Sediments. 



Since Cretaceous times this portion of Tasmania appears 

 to have been enjoying sub-aerial conditions, and no signs 

 of Tertiary sedimentary rocks wei-e seen. A little Pliocene 

 (?) basalt occurs at Mayne's selection, six miles west of Fitz- 

 gerald, as shown on Mr. Twelvetrees' and Mr. Reid's maps. 

 Pleistocene glacial deposits litter a great part of the country- 

 side. These will be described in the next section. Post- 

 Tertiary alluvial deposits exist in the Russell Falls River 

 Valley (Twelvetrees, 1908) and on the lower Weld, at the 

 mouth of which there is a curious delta of alluvial material 

 stretching some three miles up the river and three miles 

 along the bank of the Huon, consisting of small, round, 

 water-worn pebbles, chiefly of quartzite, and is more or less 

 swampy ground. This appears to be a flood plain of the 

 Weld, deposited as the swift current was slackened as it 

 C 



