BY A. N. LEWIS. M.O., LL.B. 23 



Mt. Anne. This looked like rocks of this or the succeeding 

 system, but their actual nature could not be confirmed. Here 

 as elsewhere the Permo-Carboniferous mudstones are suc- 

 ceeded by the Knocklofty sandstones of the Trias-Jura. 



The Russell Falls River is cutting through the upper 

 marine series of the Permo-Carboniferous, which is traversed 

 at intervals by bai's of diabase and overlaid at about the 800 

 foot contour round the valley by Trias-Jura sandstones 

 through which the river has cut and which are now nearly 

 all denuded away, leaving the diabase of the hillsides bare. 

 Elsewhere in the area, if the older rocks were ever covered 

 by these sediments erosion has "-ow removed all trace of 

 them. 



(d) The Diabase Intrusions. 



The reader is referred to Mr. P. B. Nye's remarks on 

 the occurrence of the Cretaceous diabase in his "Under- 

 ground Water Papers, Nos. 1 and 2," undoubtedly the best 

 account of the subject yet published. The area described in 

 this paper would repay detailed study on this point. 



In Tasmania the diabase appears to occur either in 

 laccolith-like mountains of greater or less extent such as 

 are common in the centre, east, and south, and of which the 

 Central Plateau, Mt. Field East, and Mt. Wellington pro- 

 vide examples, and which may be distinguished by the 

 immense beds of Permo-Carboniferous and Trias-Jura sedi- 

 ments hoisted up on their flanks, or, more rarely, as moun- 

 tains isolated by erosion from a once extensive sill of diabase 

 which spread over the top of early Palaeozoic rocks, for 

 example. Barn Bluff', the Eldon Range, and most of the 

 more western diabase mountains (see The Geological Sur- 

 vey's publication "Ccal Resoui'ces of Tasmania," 1922). 



The Snowy Mountains, Mt. Styx, Marriott's Look-Out, 

 and the diabase hills south of the Tyenna Valley are of the 

 laccolithic type and probably are connected with the Mt. 

 Wellington range intrusion. Probably diabase has covered 

 beds of the older quartzites along the edge of the known 

 occurrence of these, and this is undoubtedly the case on 

 the lower Weld and west of Tyenna, but it is difficult at 

 present to say where the main upthrust of the diabase 

 occurred and where the sills joined the laccolithic intrusions. 



Mr. Twclvetrees has classed the diabase of Mts. Mueller, 

 Anne, and Wedge as portions of sills (Twelvetrees, 190S). 

 This certainly appears to be the case in regard to Mt. Anne 

 and Mt. Wedge, but Mt. Mueller and Mt. Weld seem rather 

 to belong to the laccolithic type with extensions westward in 



