Glacial Kangaroo (juUi). 879 



Peti''Ograp!iical Characters of the Matrix of the Deposit. 



As soon as 1 saw the deposit, even tlie superticial portion, I 

 recognised tiie great resemblance of the matrix to an nltra-basie 

 volcanic agglomerate. In hand specimen it is in snww ways com- 

 parable to the material tilling the volcanic neck at tlie Pennant 

 Hills, near Sydney, New South Wales. 



The microscopic and chemical evidence, it will be seen, entirely 

 supports this view of its origin. As an example of the matrix at the 

 surface one may cite an agglomerate (Plate xxxii., Fig. 2), occur- 

 ring 40 yards south of the north end of the deposit. Glacial pebbles 

 occur in this material. Under the microscope, (Sections No. 1009), 

 there are seen large fragments of angular quartz, more or less cor- 

 roded, and of Oidovician shale. Some secondary quartz filling 

 <avities in the rock or replacing primary minerals can also be 

 distinguished. The bulk of the rock consists of larger and smaller 

 fragments of a very basic volcanic rock embedded in a finer volcanic 

 paste or cement. Both fi-agments and cement are much altered, 

 so that the ruck is stained and impregnated with red oxide of 

 iron. 



The minerals present in the rock are olivine, now represented by 

 pseudomorphs in serpentine, biotite in long lath-shaped crystals, 

 now bleached and partially altered to liydromica, augite (?), pos- 

 sibly represented by granular iron-stained crystals, magnetite or 

 ilmenite, and a base which is almost isotropic, and may i-epresent 

 glass or possibly analcite. The rock is essentially an olivine- 

 biotite-nionchiquite agglomerate, with fragments of quartz and 

 Oidovician sediments. It resembles closely the monchiquite dyke 

 which inter.sects the deposit, but differs mainly in tlie paucity or 

 absence of augite. 



As examples of the nature of the deposit below the surface, the 

 following specimens may be described : — 



Specimen from the main shaft (Section No. 1010), (Plate xxxii.. 

 Fig. 3). For chemical analysis, see below. 



The rock is much altered. Porphyi-itic pseudomorphs in serpen- 

 tine after olivine are abundant, the ground-mass showing granules 

 and prismatic purple needles of titaniferous augite, and a colour- 

 less to brown isotropic matrix, which may be glass or analcite. 

 Small water-worn and angular quartz grains occur, and are cor- 

 roded, and some show a reaction rim, including minute prismatic 

 needle.s, possible of hornblende. Some secondary silica occurs in 

 the form of quartz and chalcedonic infiUings or replacements. The 



