(icohxjil of Liltl<liil<'. Ml 



1. The dose pioxiniity ui intrusions of gijinodioiite poiplix iv 

 in the subjacent Silurian, at lower levels than the schistose rock, 

 suggests tliat the alteration is dut- l<> those ami lii<l<lcn plutonic 

 intrusions. 



2. The Silurians beneath the schistose dacite have Vjeen alti-icl 

 into hornt'els, which is an extreme product ot" thermal meta- 

 niorphism, and it is impossible to doubt that the altered dacite 

 must be referred to the same cause as the horufels. 



Regarding the irregularity of the distribution of schistosity thai 

 has been noted in the small area under discussion, the prevalenif of 

 the big granodiorite dykes suggests the explanation that tliese 

 anomalies are due to the unequal distance of the dacite from these 

 intrusions, and possibly also to their unequal distance from the 

 cooling surface. 



B.— The Plutonh- Piiask. 



The dacite forms a sliarp junction with the granodiorite. soiiih 

 of the Gembrook railway line, and for six or seven miles along the 

 contact, the former has been converted int<j a band of gneiss, pene- 

 trated in several places by veins of pegmatite and quartz. For 

 these reasons. Prof. Skeats (13), in describing the above meta- 

 niorphism of the dacite, concludes that tlie dacite is older than the 

 granodiorite. Corroborative evidence obtained by Prof. Skeats at 

 Macedon. Warbiirton. Xyora, and Maivsville, confirms this con- 

 clusion. 



Comparison of the chemical analyses of the dacite and of the 

 granodiorite has shown that they are almost identical in composi- 

 tion , and are therefore leferable to the same source, and to the 

 same period. (13). 



C. — TiiK IIypabyss.vl Ph.\sk. 

 In the district shown on the map, two gioups of dykes stand 

 out prominently, one along tlie western ])order of the volcanic 

 rocks, the other along the eastern bordei-. Tlie former group are 

 characteristically basic, the latter intermediate in chemical com- 

 position. For reasons given below, the former are treated as 

 'differentiated, and the latter as undifferentiated dykes. 



a. — The Differentiated Dykes. 



These form a group of four along the western border of the 

 system. They all penetrate the volcanic rocks, but two of them lie 

 outside the area of the map. They may all be called Augite Olivine 



