BY THE REV. \V. B. CLARKE, M.A., F.G.S., &c. 301 



The loss of colour is like that of the rocks at Wildenstein, and 

 the strata lines, which are distinctly marked at Meriberi, have a 

 zig-zag course, and the prisms on the south side cut them ob- 

 liquely at angles of 62, 68, 73, dipping N.N.W. The height of 

 the rock above the sea at the quarry is 207 feet on the north side, 

 and 214 feet on the south side. The opening strikes S., 70 W., 

 and the breadth is 50 paces. I give these measurements to 

 show that an ample space has been cleared to exhibit fully all the 

 phenomena. That the prisms have probably been formed, as is 

 usual in such cases, at right angles to the intruding basalt, and as in 

 numerous cases quoted by Delesse, is shown by the way in which 

 they dip. Near St. Catherine's School, the imperfect prisms also 

 have a partia]ly fan-shaped arrangement in a dome-like mass. 

 At Meriberi the vertical portion is removed, but on the height 

 south of the opening, the summits of prisms occupy some space. 

 The unaltered rock contains casts of stems of plants ; but none of 

 these are seen in the altered rock. They have been probably all 

 obliterated by partial fusion of the silica, for it is well known that 

 silicification destroys very often the delicate parts of organic 

 structures so transmuted, as Dr. Duncan has recently found in 

 examining the silicified fossil corals of the West Indies. 



As the quartz pebbles .are only slightly altered, it is clear that 

 the heat radiating from the trap never was so great as to completely 

 fuse the silica, or dissolve it entirely. And I, therefore, believe 

 that the heat was hydrous, as all such changes must be at first. 

 An examination of the unaltered rock is necessary to understand 

 the amount of change. I submitted 619 grains of a column from 

 Meriberi to absorption, and the weight gained was three grains. 

 Some of our Hawkesbury sandstones are so incoherent, that when 

 the blocks from the Railway cutting on Darling Causeway, at the 

 head of the Grose River, are thrown over the embankment, many 

 of them crumble to powder. The sandstone near Meriberi is not 

 quite so loose as this ; but some of it consists merely of particles 

 of semicrystalline quartz, without any visible cement, which of 

 course are easily separable. This explains why the summits of 

 the fractured cliffs, themselves huge quadrilateral columns, to the 

 south of the quarry are strewn with quartz pebbles, the relics of 

 destroyed beds of loosely aggregated grit and sandstone. At this 



