Victorian Igneous Rocks. 293 



It will Itc sL't'ii that this analysis of I'pidiorite, uven when re- 

 •calculated to !()() per euiit.. winild nut cunforn) to the variation 

 •diagram of the Victorian Palaeozoic series. 



The epiiliorito, then, is elcai'ly not r-olated to the granite in a 

 serial manner, and although the evideiue is strongly in favour of 

 the two rocks being derived from a conmion magnui, they fail to 

 show any chemical or mineralogical relationship to one another. 



It is suggested that these two rocks were derived from a eonnnon 

 magma by complementary differentiation, and that the basic 

 difiterent iatioii i^ioduct was intruded to the south, and the acid 

 portion to the ncu'th. At the time of intru.sion the differentiation 

 was not (juite eonipleto, and in the southi'rn area the residual aeid 

 portion separated out, and was intiuded through the basic portion 

 in the form of a dyke. The irregular character of tlie juiution 

 ■of the granite and epidiorite at the Dog Rocks suggests the possi- 

 bility that in this ease the completion of the differentiation took 

 place insifu. 



In the Heathcote area is a somewhat analogous occurrence. Tlie 

 rocks described from this area include diabase, porphyrite, diorite 

 and an acid rock variously called aplite, granophyre, fine-grained 

 granodiorite and micro-granite. 



Professor Skeats (14) holds that the micro-granite is genetically 

 related to the diabases and represents an acid residuum from the 

 basic magma. 



The diorite is not at all normal, and probably represents a hybrid 

 rock duo to a mixing of the diabasic and micro-granitic magmas. 



One point of considerable importance is the absence in both 

 •cases of normal intermediate types. Harker (4), in discussing the 

 North British Tertiary Province, mentions the occurrence of ultra- 

 basic rocks, the eucrite group, and basic rocks associated with 

 granites and granophyres, but points out that it is a broken series, 

 types of mean acidity being al)sent. 



Anothei- interesting case of the association of acid and basic 

 rocks without the presence of intermediate types is that of the 

 laccolithic sheet of Sudbury, desei-ibed by Coleman (1) and referred 

 to by Harker (4). 



While the latter considers that the separation out of the sulphides 

 from the norites was probably due to the limited miscibility of the 

 sulphide magma with the silicate magma, he doubts whether the 

 .separation of the norite from the overlying acid rocks may be 

 oittributed to the same cause. 



7a 



