GEOLOGY AND PETROGRAPHY OF THE PROSPECT INTRUSION. 485 



minute cracks in the felspar generally clear and colorless ; 

 and in well rounded masses of from \ to 2 mm. in diameter, 

 having a cloudy yellowish appearance under the microscope. 

 The former kind was reckoned as felspar in the determin- 

 ation of the proportions of the minerals. Some of the 

 rounded masses have small aggregates of augite and 

 ilmenite surrounding them. There is little doubt they are 

 small spherical vesicles with an infilling of analcite, and 

 that the small crystals of augite and ilmenite adhered to 

 the bubbles at an early stage of the crystallisation of the 

 magma owing to surface tension. In this slide there occurs 

 a fragment of quartz measuring 3Jby 2 mm. as represented 

 in fig. 1, Plate XXXIX. It is probably derived from the 

 shale, and is surrounded by a zone of alteration products, 

 apparently partly actinolite. 



The order of consolidation is practically the same as that 

 of specimen B from the Reservoir Quarry. 



Specimen M. 

 Localitij. S.E. corner of Emu Quarry, a few metres west 

 of specimen L, at the junction, actually in contact with 

 the shale. 



Megascopically bluish-grey in colour with angular black 

 inclusions. The rock effervesces strongly with acid in 

 every part. 



Microscopic examination shows that this rock is a pecu- 

 liar product of alteration, containing so much calcite that 

 it occupies an intermediate position between a basalt and 

 a magnesian limestone. 



The constituent minerals in order of decreasing abund- 

 ance are now as follows: — calcite and dolerite, felspar 

 (andesine), chlorite, and a little serpentine. The rock was 

 probably originally very similar to specimen L above 

 described, though, since the felspar possesses low extinction 

 angles and appears to be andesine, we may conclude that 



