STRUCTUKE AND COMPOSITION OF A BA.SALT FROM BONDI. 231 



from the direction of Greenwich. The basalt contains traces of 

 chromium. 



A needle of the basalt is susceptible of permanent magnetism,, 

 and when swung freely will act as a magnetic needle. 



Explanation of Plates. 

 Plate IX. i 

 Fig. 1. — View of a fissure left by the decomposition of a previously 

 existing dyke, Bondi. The lower portion of the fissure is filled with 

 decomposed basalt. The figure shows characteristic weathering of the 

 Hawkesbury Sandstone. From a photograph by the author. 



Fig. 2. — Prismatic or columnar sandstone, Bondi. The columnar 

 structure was induced by the intrusion of the heated igneous dyke. The 

 columns are about one foot in diameter. From a photograph by author. 



Plate X. 



Fig. 1.— Microscopic structure of Bondi basalt. The porphyritic figure 

 in the centre of the field is an augite. 



Fig. 2. — Microscopic structure of Bondi basalt. The centre of the field 

 shows an olivine crystal, penetrated by a bent wedge-shaped intrusion 

 of the ground mass. From micro-photographs by the author ; both 

 figures magnified 30 diameters. 



Plate XI. 



Fig. 1.— Crystals of sodium chloride formed in a weak hydrochloric 

 solution of soluble portion of Bondi basalt. Magnified 35 diameters. 



Fig. 2. — Sodium chloride crystals, magnified 35 diameters, formed by 

 etching one square inch of Bondi basalt with strong hydrochloric acid. 

 Figures from micro-photographs by the author. 



Plate XII. 



Fig. 1. — Twin of olivine, magnified 30 diameters. 



Fig. 2.— Corroded olivine, some of the faces are idiomorphic. The 

 other faces have been attacked by the molten magma, magnified 30 

 diameters. 



Fig. 3. — Olivine with glassy inclusions. 



Fig. 4. — Six sided mineral not identified. Probably microsomite, 

 magnified 500 diameters. 



Fig. 5. — Corroded augite, magnified 30 diameters. 



Fig. 6. — Characteristic olivine, magnified 30 diameters. 



Fig. 7. — Augite showing a secondary growth, in which is embraced a 

 lath of felspar, magnified 40 diameters. 



Fig. 8. — Zoned augite, magnified 35 diameters. 



Fig. 9. — Broken crystals of olivine, magnified 40 diameters. 



Fig. 10. — Secondary growth in an augite crystal, magnified 40 diameters 



Fig. 11. — Streaming of felspars around olivine, magnified 45 diameters. 



