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well known on the Coast, in the Blue Mountains and elsewhere. 

 It is sometimes very pebbly and becomes a conglomerate. 

 The rolled quartz grains have genei'ally received a fresh 

 supply of silica since the consolidation of the rock, and now 

 exhibit more or less crystal form. It is the reflection of light by 

 these crystal faces that occasions the glistening appearance of 

 the sand on the roads about Sydney. It sometimes contains 

 flakes of graphite. Small garnets also occur. 



Narraleen Beds. — Shales, sandstones, and conglomerates 

 exposed to some extent in the cliffs between Narrabeen and 

 Lake Macquarie, but known best in the various bores that have 

 been put down through it, and in the shaft at the Balmain 

 Colliery. The conglomerates are sometimes very pretty, through 

 containing coloured jasperoid pebbles. In places the beds 

 become copper-bearing (assays up to two per cent, have been 

 obtained). Beds of volcanic tuff and heavy sand containing 

 zircon and magnetite also occur. 



Cores from some of the bores that have been put down stand igneous Eocks. 

 in the corner to the right of the entrance. 



These consist of narrow dykes usually of olivine basalt, 

 containing analcite in some cases, frequently occupying joint- 

 fissures that cut across the sedimentary strata, and sometimes 

 sending of£ small lateral offshoots. These dykes are more easily 

 decomposed than the sandstone, in consequence of which their 

 presence is indicated by white clay, or by a ravine with 

 precipitous sides. At Long Eeef, INTarrabeen, an amygdaloidal 

 dyke of diabase may be seen on the coast at low tide, standing 

 up as a low wall. The occurrence of these dykes is best illustrated 

 at Bondi, where ravines partly occupied by clay, and a boss of 

 undecomposed basalt, occur. These dykes have injured the coal- 

 seams, as was proved by the first bore put down at Cremorne. 

 In addition to these dykes, more or less cii'cular orifices (pipes), 

 filled with basalt, or with volcanic breccia, occur. As an example 

 of the first may be mentioned the blue-metal quarry at Dundas ; 

 of the second, the Yalley at Springwood, the Basin, near Penrith, 

 and Old Man Yalley, near Hornsby Station. 

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