■350 Morris Morris: 



(Allot 30'^). 5 feet wide. Both are nmcli decomposed, the latttT 

 being now a soft, gritty rubljle. Both strike about ."} deg. west of 

 north. 



b. — The Undifferentiated Dykes. 



These dykes all occur either penetrating, or closely associated 

 with, the remains of the igneous rocks that form a broken border 

 along the eastern side of the Evelyn fault. 



They fall into two divisions : (1) the Wandin dyke. (2) the grano- 

 ■diorite porphyries. 



(1) The Wandin Dyke. — This dyke lies aljout 1| miles due west 

 ■of Wandin (Allot. 33* and 3) in the series h. It outcrops spora- 

 dically for H miles, and with an average width of about 45 

 to 50 feet. It bears a very close resemblance to the propylitizt-d 

 Dacite dyke of the Macedon district (one mile Avest of Hesket) (1.")). 

 The chemical analysis of the latter is probably very close to that 

 of the former, and has been used for that reason in the variation 

 diagram, Avhere it conforms very w^ell with the curves. 



This is a granitic-looking rock, with numerous phenocrysts of 

 felspar and dark biotite, set in a fine ground mass. 



There are large idiomorphic phenocrysts of zoned plagioclase, 

 biotite, and probably another mineral now chloritised. Smaller 

 irregular-shaped crystals of orthoclase are numerous. The rest of 

 the rock consists of a micrographic intergrowth of quartz and ortho- 

 clase, Avhich surrounds the phenocrysts. The plagioclase is sharply 

 marked off from the eutectic corona, but the orthoclase often passes 

 into it by a gradual transition. Apatite is common; zircon and 

 magnetite are sparingly present. The granophyric structure, which 

 is due to pneumatolytic action on the ground mass, supports 

 Becker's suggestion, " that the ground mass of a porphyritic rock 

 tends to approximately eutectic composition. ''i 



(2) The Granodiorite Porphyries. — These form a group of dykes, 

 lying west of South Wandin, on the high hornfels shoulder of the 

 Dandenongs between Olinda Creek and the Evelyn fault. As ilia 

 structure here contains several interesting features, a more par- 

 ticular description is given. (Plate XXX., Figs. 3 and 4.) The 

 Evelyn fault is marked in this part by a deep depression, which 

 •develops into two valleys, one north, the other south of a small 

 watesrshed in the depiession. The dacite is sharply severed from 

 the hornfels by these two fault valleys, except at the watershed, 



1. See (19) p. -264. 



