210 REV. J. MILNE CURRAN. 



Slice 38. — Leucite Basalt from Harden, New South Wales. 

 In hand specimens, this rock appears as an exceedingly fine- 

 grained basalt with very minute sparkling crystals, suggestive of 

 these rocks. Where a thin slice is made and placed under the 

 microscope the first characteristic noted, will be the entire absence 

 of felspars. There are certainly lath-shaped prisms in the rock, 

 but, on due examination they prove to be augites. Augite also 

 occurs as a micro-porphyritic ingredient. Plates of a finely striated 

 mica are also present. The whole character of the rock and a 

 rather peculiar appearance of the olivines in particular, remind one 

 of the leucite rocks from El Capitan and Byerock, New South 

 Wales. The El Capitan rocks have been described by the writer, * 

 Mr. (now Prof.) T. W. E. David, b.a., and Mr. W. Anderson. f 

 The Harden rock resembles, in general microscopic characters, 

 the leucite basalt from El Capitan. The micro-photograph ex- 

 hibited gives a general idea of the rock magnified to thirty 

 diameters. The minerals porphyritically developed, are, leucite, 

 olivine and aggregates of magnetite. The ground-mass consists 

 of granular aggregates of leucite, augite, and magnetite. The 

 leucite is fairly abundant in the slices, showing as usual, the radial 

 and concentric inclusions, that seem to characterise this mineral 

 wherever it is found. Good examples of this structure will be 

 readily found in the sections. The micro-porphyritic olivines in 

 every instance show signs of decomposition into a yellowish-green 

 serpentinous matter. It is very probable that the mica is a 

 secondary product in this rock. Leucite basalts are rocks, so very 

 rare, that this additional occurrence in New South Wales is of 

 great interest and important enough to justify a separate memoir 

 on its distribution, and structure, as soon as the material collected 

 can be worked up. 



Slice 39. — Leucite Basalt from Harden, collected about half a 

 mile from the last slide. This rock is, without doubt, from a 

 tertiary basalt flow. In Europe and North America leucite is 



* Proc. Linn. Soc. N. S. Wales, 1887, Vol. n., p. 974. 



f Rec. Geol. Survey N. S. Wales, Vol. i., 1890, Part iii., p. 153. 



