362 Morris Morris.- 



narrow strip from Lilydale across Cave Hill, which was done 

 by V. R. Stirling. Some of his boundaries, and those of the 

 geological map of Victoria, ijublished by the (Teological Survey De- 

 partment, have undergone important alterations during revision. 



2. A denuded synclinal fold of the Yeringian (U. Sil.) series 

 forms the basal rock of the district. Their strike is normally north 

 and south, but in the area north-east of a line joining Lilydale and 

 Evelyn, it is diverted 40 deg. or 50 deg. to the east. 



The prevalence of littoral facies probably marks the close uf the 

 Silurian invasion. 



The alteration of sonie facies into quartzite has been caused, not 

 by thermal metamphorism, but by metasomatic processes, aided 

 probably by folding stresses. 



3. Upon this sedimentary floor, lies a stack of igneous rocks, 

 which have lieen linked up into one system with those of the 

 Dandenong Ranges. 



These rocks are regarded as representing the volcanic phase of an 

 igneous cycle, which was completed by plutonic and hvpabvssal 

 phases. 



Representative specimens selected from tlie tliree phases have been 

 described and compared. 



The volcanic rocks are resolved into five series, and these series 

 are regarded as being consanguineous. 



The chemical composition of the first four series Avas determined 

 by means of analyses specially made by Messrs. Bayly and Hall. 



Variation diagrams have been made from these and other analyses 

 of rocks, selected from each of the three phases of the cycle. 



The bearing of this evidence on the differentiation of the parent 

 magma is discussed. The differentiation was progressively less 

 acid. 



The composition of the parent magma of the differentiated vol- 

 canic series is shown to be represented by the last series of the phase 

 (viz., Hypersthene Dacite), which remained on the whole un- 

 changed throughout tlie |)lutoiiic and liypal)yssal phases of the 

 cycle. It was sub-alkali, and between acid and intermediate in 

 composition. 



Of the volcanic series, the first foui-. which are differentiated, 

 fall naturally into two pairs : — 



(i) A pair of toscanites (or alkali daciti's). These ai'e clu'iiiiially 

 identical, but mineralogically dissiiiiilai'. 



This difference is attributed to mineralisers (especially H.,0), 

 present in the Lower, but absent from the Upper. 



I 



