Norman Taylor — The Cudgegong Diamond Field. 411 



a pale green colour, and a rough parallelism in rings round the con- 

 cretions. It generally weathers brown, though the more felspathic 

 varieties have the external appearance of granite. It effervesces in 

 joints and minute fissures with hydrochloric acid, and contains traces 

 of a dark brown mica (?). The decomposition of the protoxide of 

 iron in the hornblende, and the partial removal of the lime and 

 magnesia, confer great fertility on the soil derived from the green- 

 stone ; and the highest ranges in the neighbourhood which consist 

 of this rock are always clothed with open timber and fine grass, in 

 contradistinction to the Silurian ranges, which are rocky, scrubby, 

 and thickly timbered. To the decomposition of the greenstone is 

 also due the large quantity of magnesite which occurs — in fact, 

 grows— round the waste heaps at the mouths of the shafts. The 

 white clay turned up soon becomes covered with small spherical 

 nodules, which aggregate in time into a solid botryoidal mass of 

 mixed carbonates of lime and magnesia. This only happens super- 

 ficially, and where the clay has had access to the atmosphere. 

 There seem to be two varieties of this mineral (one of which may 

 be derived from decompdsing basalt) as well as a mineral resembling 

 common opal, also showing externally that it is an aggregate of 

 spherical nodules. An analysis of the last, made by the late Pro- 

 fessor Thomson, proved it to be a pure hydrated carbonate of 

 magnesia, with specific gravity 2-94, and containing — 



Magnesia 46-99 



Carbonic acid 4978 



Water 4-08 



100-85 



The greenstone possesses two systems of joints, — one striking 

 north and dipping west, — the other striking E. 30° N. and dipping 

 N. 30° W. It was for some time mistaken by the diggers for basalt, 

 and sunk in to some depth. A quartz-vein intersects it, south-west 

 of Buckley's, containing galena, out it had not been opened up. 



Along the foot of the range, on the west side of " the flat," is a 

 series of beds, about ten chains wide, having the same strike as the 

 slate rocks. It consists of flinty shales and a thick hard brecciated 

 conglomerate, full of nodules, like amygdaloids, of crystalline lime- 

 stone, which decompose out on exposed surfaces, and give the rock 

 a vesicular appearance. This breccia also contains fragments of 

 flint, red felspar, etc., in a greenish siliceous base. It shows no 

 bedding planes and passes to the west, by insensible gradations, into 

 a rock of a granitic character, full of felspar crystals, with specks of 

 iron pyrites and galena, and much resembles a felstone porphyry. 

 There seems to be a great similarity between these beds and those 

 in Ireland, described by Jukes as ash-beds. The flinty shales have 

 a peculiar system of joints or false-bedding, at right angles to the 

 strike or real bedding, which latter is seldom distinctly seen. These 

 highly altered shales are characteristic of greenstone intrusions, for 

 they, in every instance, occur as the contact rock, both in New 

 South Wales and Victoria. 



The river, at the north end of the " Two-mile-flat," runs westerly 

 across the strike till it reaches the above-mentioned beds, when its 



