ALMANDINE GARNETS FROM THE HAWKESBURY SANDSTONE. 49 



and magnetic, and had they originated from that source we might 

 have expected to have found them black or dark brown in colour, 

 as for instance the variety Melanite from Vesuvius. The evidence 

 already obtained, points to the fact that granite was the principal 

 rock from which the Hawkesbury Sandstone was derived, and it 

 shows the persistent nature of these garnets that they should 

 have withstood decomposition in such fragments, when so readily 

 cleaved, a property not of common occurrence in garnets. 



The most prolific sources of the garnet, however, are the meta- 

 morphic rocks, these crystals being found plentifully in mica-schist, 

 chlorite-schist, gneiss, limestone, &c. When writing on the 

 Hawkesbury Sandstone, the Rev. J. E. Tenison- Woods* inclined 

 to the opinion that considerable masses of the sandstone had been 

 subjected to metamorphic action, basing this suggestion upon the 

 presence of the glistening particles of crystalline quartz, and 

 mentioning the millstone grit of England as an example. Even 

 if this opinion is acceptable, there is nothing to show that these 

 garnets are the effect of this metamorphism ; they are simply an 

 accidental constituent of the conglomerate in which they are 

 found, they are not in crystals, and had been submitted to fracture 

 before they became stationary. There is nothing to denote that 

 they are of more recent date than the surrounding rocks. 



The specific gravity of the garnets is 3*902. Hardness, just 

 above 7, being just hard enough to scratch quartz with difficulty, 

 they were mounted in lead for this test. 



Before the blowpipe they fuse readily, the bead being magnetic. 

 With borax they give an iron reaction ; with soda show presence 

 of trace of manganese. When examined in thin sections they are 

 seen to be isotropic, no light passing during an entire revolution. 

 For this investigation the small stones were placed in a glass 

 tube closed at one end, heated and pressed flat between two 

 pieces of wood ; when cold, they can be ground down and mounted 

 in the usual way for rock sections. 



* Proceedings Royal Society, N. S. Wales, Vol. xvi., p. 53. 

 D— June 6, 169-4. 



