and their Contact Zones. 47 



most, an intrusive mass, seemingly latest in age of all, 

 and which is almost wholly composed of a mineral 

 which I have referred to amphibole-anthophyllite. I 

 have already so fully described the characteristics of this 

 rock-forming mineral, and also of the associated mineral 

 species, that but little remains to be said excepting to indi- 

 cate the position which it seems to me should be assigned to 

 the rock itself in the petrographic system. It has many 

 resemblances to gabbro, but the departure from gabbro is in 

 the occurrence of an amphibole mineral instead of diallage. 

 Many of the normal gabbros are characterised by a prepon- 

 derance of a monoclinic pyroxene, having a pinacoidal 

 cleavage, associated with an accessory orthorhombic pyroxene. 

 This abnormal gabbro has preponderating monoclinic amphi- 

 bole having a pinacoidal cleavage, and has an accessory 

 or orthorhombic pyroxene. For such a compound a special 

 name is still wanting, and the most appropriate, although 

 cumbrous, one would be amphibole-gabbro.* Such a rock 

 stands to diorite much as the normal gabbro does to diabase 

 and melaphyre. 



(d.) Dykes. 



In speaking of the dykes of the district, I have found it 

 most convenient to depart somewhat from the general plan 

 of this essay, and to describe each of the classes from typical 

 instances rather than to enter first upon a description of the 

 component minerals. 



The dykes of the district include the classes felsite, 

 diorite, and diabase. The former are met with in the eastern 

 part traversing the metamorphic schists, and their age is 

 quite uncertain. A few also occur throughout the western 

 part of the area described. They are often granular and 

 quartzose, and are then often much decomposed, and generally 

 have a resemblance to the dykes of granular felsite common in 

 the neighbourhood of Omeo. Elsewhere, as at Sheep Station 

 Creek and the lower part of Riley's Creek, they are compact, 

 hard, grey or bluish in colour, and seem externally but little 

 affected by the agencies which have decomposed the adjoin- 

 ing granites or diorites. Thex diorite dykes are met with 

 most commonly in the tracts surrounding the intrusive area, 

 but also traverse parts of it, as, for instance, the quartz diorites 



* Streng has described a hornblende- gabbro from Dulutb, U.S.A. See 

 Neues Jahrhic/i, 1877, p. 113. 



