158 Proceedings of the Royal Society of Victoria. 



100.41 101.10 99.96 



Sp.G. 2.778 2.637 



I. "Metamorphosed Sediment," analagous to adinole, allotment 



12, Parish Crosbie. Howitt, A. W., " Notes on Diabase 

 and Adjacent Formations of the Heathcote District," p. 8. 



II. The same, No. 18 Gatehouse, at Heathcote. Howitt, A. W, 



0/>. cit., p. 8. 



III. Adinole, Heinrichsburg, near Magdesprung. Harz. H. 



Rosenbusch, " Elemente der Gesteinslehre," p. 333. 



IV. Adinole, Gitzhiigel, near Hasselfelde. Harz. H. Rosenbusch, 



Op. cit, p. 333. 



The acid igneous rocks have been carefully described by Mr. 

 Howitt, who states that " I have felt much difficulty in assigning 

 a place in classification to these granitic rocks." (6, p. 5.) He 

 finally called them aplites and suggested for them the provisional 

 term of plagioclase-aplites. With Mr. Howitt's determination of 

 the mineral constituents and structure of these rocks I entirely 

 agree. There are two distinct varieties of rock. The first— 

 those identified as aplites- — consists of orthoclase in eroded and 

 altered crystals, idiomorphic crystals of plagioclase, rounded 

 grains of quartz, and flakes of colourless mica. The plagioclase, 

 as Mr. Howitt remarks, is " more or less completely replaced by 

 flakes and rosettes of a colourless mica." Biotite is also present 

 in small patciies. 



In the second variety of rock — Mr. Howitt's labradorite- 

 porphyrite — the structure is porphyritic, and the base is grano- • 

 phyric. The colour of the rock is dark grey to bluish or blackish 

 grey. Plagioclase occurs both in phenocrysts and in radial tufts. 



0) This sample lost .20 per cent, on drying at 212 deg. F. 



