Geolugj oj Mooi'oodac. 97 



Thk Gkano-Diokite and Apophysks of Mount Eliza. 



The Apophyses. — The-se have only been noticed in the meta- 

 niorphosed shites and sandstones of the large Moomoduc quarry, 

 about three-quarters of a mile north of Moorooduc railway sta- 

 tion. They consist of acid extrusions from the plutonic maiss, 

 and vary from tine-gi-ainedaplitic- rocks to fairly coarse pegmatites. 

 The largest vein seen measured about three feet in width. They 

 are all somewhat decomposed, and on that account no rock sec- 

 tions have been made from them. In places quartz and felspar 

 alone are present, in others biotite and nmscovite also occur, 

 usually in large flakes up to three-quarters of an inch in length, 

 and in one or two cases black tourmaline was noticed. 



Mr. Kitson has drawn attention' to the most interesting 

 feature in connection with them — viz., the general concentration 

 of the mica along the walls of the veins, the central parts being 

 relatively free from that mineral. The small sizes of the veins 

 makes it impi'ol)al)le tliat C(jiivection currents have played any 

 pait in the marginal grouping of the micas. This arrangement 

 may be referred to as an illustration of a process tirst investigated 

 by Soret'^ in tiie case of crystallization from aqueous solutions. 

 He showed that if a constant difference of temperature is main- 

 tained between two parts of a ves.sel containing a saturated 

 solution, crystallization will proceed at tirst only in that part of 

 the vessel which is at the lower temperature. Mr. TealP has 

 sought to explain the concentration of the earlier formed basic 

 minerals on the walls of some ingenous intrusions in terms of 

 Soret's principle. 



The disposition of the mica flakes in the acid veins of the 

 Moorooduc quariy may probably be referred to the same cause. 



Tlie Grano-diorite. — The plutonic mass of Mt. Eliza extends 

 as a somewhat elliptical shaped mass ju.-t over two miles long 

 from N.E. to S.W., and about a mile across in the widest part in 

 a N.W. S.E. direction. Most of this area is covered with a 

 mantle of granite detritus, and only two or three limited out- 

 crops are seen of the rock " in situ. ' The best exposure occurs 



1 Op. cit. 



2 Ann. Chim. Phy., Paris, 1881, (.'>) 22, p. 203. 



3 British Petroijraphy, p. 402. 



