BY THE REV. J. MILNE CURRAN. 22o 



decomposition. I have not met with an instance where the 

 alteration is complete. The green serpentinous matter follows the 

 cracks and cleavage lines and gradually eats its way across the 

 intervening spaces. The micro-photographs on PL xiv. figs. 2 and 4 

 show this change clearly enough. 



The edges of the olivines are sharply defined and show little or 

 no signs of corrosion. The form of the crystals does not seem 

 affected in any way by the surrounding minerals, so that, to use a 

 term of Rosenbusch's, they are for the most part idiomorphic. 

 Inclusions of magnetite are common, as well as patches of a semi- 

 devitrified glassy base. It is more than probable that some of the 

 large olivines were formed at a depth and floated up before the 

 pecond generation of olivines consolidated. On PI. xiv. fig. 1 will 

 be noticed a crystal of olivine that was broken along a central 

 line ; one half is seen in the micro-photograph, and the other half 

 is found on another part of the slide. 



Augite. — The augite in the Bathurst basalt is not penetrated by 

 the felspars, so as to give rise to an ophitic structure. But the 

 consolidation of the augites must have been subsequent to that of 

 the felspars. The augite is sometimes to be seen partly moulded 

 around the ends of the laths of plagioclase. An example is shown 

 on PL xiv. fig. 5. Here a large zoned augite is seen partially 

 penetrated by a felspar as if the latter was forcibly carried against 

 the augite when the pyroxene was still in a plastic condition. 



On slide 41 an augite will be found with well defined edges. 

 It shows a figure in convergent polarized light. Faint traces 

 of cleavage lines seemingly parallel to the prism can be 

 detected, so that it is evidently a basal section. The same 

 slide shows some good examples of zoned and twinned 

 augites. On slide 46 a fine example can be found of a porphyritic 

 augite sliced in the clinopinacoidal plane. The crystal is partially 

 penetrated by a felspar, and with inclined Nicols shows the well 

 known hour-glass structure often noticed in augites. 



Felspar. — Mr. A. W. Howitt made some measurements of the 

 felspars in this basalt, and noted that, as all the obscuration angles 



