518 W. N. BENSON. 



Both these analyses fall into the division II. 6. 4. 3. with 

 raagmatic name of Hessose. Microscopically the felspar 

 was determined to be bytownite (this is confirmed by the 

 analysis), the diallage shows the development of inclusions 

 in the (010) plane as well as in the (100)— the pseud o-hypers- 

 thene of Dana. 1 It is weakly pleochroic with a and b yel- 

 lowish-green, and c greenish-grey. In places it shows a 

 well marked ophitic character (see fig. 7) a considerable 

 amount of alteration has taken place with the formation 

 of green mica and matted chlorite. A little calcite is 

 present. This rock is almost a cucrite. 



Gabbros and hypersthene gabbros occur with rather 

 more acid plagioclase (labradorite) in which ilmenite is 

 present. The constant association of this mineral with a 

 pale green serpentine with vermicular intergrowths of 

 calcite is very noticeable. The augite is not diallagic, and 

 is of pale pink-brown colour. The hypersthene is quite 

 subordinate. 



Pleonastc-hca viitij (iahhroid Rocks. 



Among the most interesting groups of rocks to be found 

 in the Dundas quarry are a group of gabbroid inclusions 

 characterised by the presence of a bluish-green spinel. 

 Thanks to the kindness of Mr. C. A. Siissmilch and Mr. 

 R. E. Priestly, who have lent me sections of these rocks, I 

 have been enabled to study a continuous series of them. 

 They fall into two distinct divisions— those in which the 

 pleonaste is granophyrically intergrown with the pyroxene, 

 and those in which it forms merely irregular grains. In 

 the latter division it is always the first mineral to crystallise. 

 The pyroxene is pinkish augite or diopside-diallage, or 

 hypersthene, paler in colour in those rocks in which it is 

 more abundant. In the following table is given the approxi- 



1 Cited by Judd, Quart. Journ. Geol. Soc, 1885, p. 380, see also Utc. at. 



