Igneous Rocks. 2(V6 



dacitic rocks from near Healesville. He believed tliat the dacites 

 were either of late Mezozoic or early Tertiary age, and he stated 

 that " At the northern foot of the Blacks' 8pui-, the dacites rest on 

 granodiorite. " He described the microscopical features of a lock 

 with flow banding from near Lindt's gateway, and conclnde<l that 

 it was a weathered dacite. 



In 1904 F. Chapmani contributed a feAv petrological notes on the 

 igneous rocks to the south of the area dealt with in the present 

 paper. He determined a gneissic banded rock consisting of plagio- 

 clase (? oligoclase), augite enwrapped by brown hornblende, and 

 hypersthene, from the Don river valley as a granulitic diorite.^ 

 Brief petrological notes on the granodiorite and dacite are also 

 given. 



A. E. Kitson^ believed that the dacite series was Upper Mezozoic 

 or Lower Cainozoic in age. 



In 1908 Professor Skeats'' summarised certain of the salient 

 features in the petrography of the dacitic rocks near Healesville, 

 Narbethong and Marysville. He determmed the volcanic and in- 

 trusive rocks to be dacites, quartz porphyrites, quartz porphyries 

 and granite porphyries, and he stated that " At Dandenong Hills, 

 Narbethong, Marysville and the Strathbogie Ranges, the dacites 

 appear to pass, by the increase of quartz and the diminution or 

 disappearance of hypersthene, into quartz porphyries and quartz 

 porphyrites. No sharp junctions have been noticed and it is 

 inferred that the change is a gradual one." 



In 1908 J. Easton,^ of the Victorian Geological Survey, made a 

 rapid survey of the boundaries of the dacite series near Heales- 

 ville, Warburton, Narbethong, etc. In a brief report mention is 

 made of the presence of normal biotite dacite, tuffs, granodiorite 

 and trachyphonolite. He records finding the latter rock at two 

 points near Warburton, but his determination of the rock is, with- 

 out doubt, erroneous, as alkaline rocks appear to be entirely absent 

 from this area. 



1 " Excursion to Lauching Place." Victorian Naturalist, vol. xx., No. 9, 1904. 



■2 In view of Professor Skeats' later work on the relations of the dacites and granitic rocks near 

 •Gembrook, it is probable that this rock is a gneissic dacite. Granodiorite and dacite come into re- 

 lation near the Don river valley. 



3 " Excursion to Warburton." Victorian Naturalist, vol. xxii., No. 8, 1905. 



4 " The Volcanic Rocks of Victoria." Pres. Add. Sect. C, Aus. Assoc. Adv. Sci., Brisbane, 

 1909. 



"Boundaries of Formations between the head of the Acheron and Yea Rivers and the Varra." 

 Rec. Vict. Geol. Surv., vol. ii., Pt. 4, 1908. 



