Vol. 51.] SECTIONS IN THE MALVEEN HILLS. 3 



A few details as to the distribution of the rocks may now be 

 given. 



Along the western boundary of the area there is a broad strip of 

 ground occupied by dolerite. A specimen from Clutter's Cave has 

 been figured and described by Mr. Rutley. 1 He says that the 

 felspars are chiefly labradorite, in laths generally corroded and 

 frequently bent; augite appears in irregular grains, few distinct 

 crystals ; ilmenite and white opaque matter, probably leucoxene, 

 and pyrites in very minute specks occur ; also a small vein of 

 epidote. I have only to add that in my slide there are vesicular 

 cavities filled with a zeolite-like mineral. For about 10 chains 

 north and 20 chains south of the Cave all the rocks seen have a 

 strong general resemblance to this one. They vary in grain and in 

 the relative proportions of the component minerals, but they are 

 sufficiently near one another to make it possible that they may all 

 belong to the same mass. 



Analyses xxxvi. to xxxviii. of Mr. Timins's paper give the com- 

 position of the rock at the Cave and rocks in its neighbourhood. 



East of this dolerite there is a belt of ground over which many 

 of the rocks have a fragmental aspect. In some slides angular 

 chips of quartz and felspars are bedded in fine dust ; others consist 

 entirely of fine dust, but their fragmental character is fairly obvious. 

 Rocks of this character, lying on the same strike, run from Broad 

 Down on to Hangman's Hill ; they are probably tuffs. On the 

 south side of Hangman's Hill, 200 yards east of Hill Cottage, there 

 is a very conspicuous crag. The rock from this is crowded with 

 small grains of magnetite and slender laths of felspar. A very 

 similar rock occurs about 100 yards to the north, in which a crystal 

 or two of augite remain unaltered. These rocks resemble very 

 closely the matrix of some of the lavas of Etna. No rock like this 

 has been detected elsewhere in the area, a fact which suggests that 

 it may be intrusive. 



Going now eastward, we come on to another belt of dolerite, not 

 differing essentially from the rock of Clutter's Cave. It was seen in 

 the cuttings made for enlarging the reservoir on its northern bank, 

 and a similar rock seemed to run along the same strike across Broad 

 Down. It appeared to die out before reaching the valley between 

 Broad Down and Hangman's Hill ; and the rocks on the same strike 

 south of that valley are of a totally different character. 



The rocks that follow to the east are of rather a perplexing 

 character, and many of them largely decomposed. A hard bed stood 

 up towards the northern end of the puddle-trench, and a rock of 

 the same character was seen on the same strike in the cutting for 

 the pipe-track. It is a very problematical rock. There may be an 

 isotropic base, but the doubly-refracting particles lie so thick that 

 it is difficult to be sure of this. The doubly-refracting grains are 

 small, have most of them no definite outlines, and polarize in dull 

 grey tints. There is a strong rhyolitic aspect, and this is probably 



1 Quart. Journ. Geol. Soc. vol. xliii. (1887) p. 498, pi. xx. fig. 9, & pi. xxi. 

 figs. 4, 5. 



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