278 ON THE TRANSMUTATION OF ROCKS, &c., 



in Queensland, similar phenomena are presented ; but in some 

 instances the alteration there may have been due to trappean 

 rather than to granitic rocks, as in the case of the flanks of Red 

 Cap and other hills on the Cogoon. 



No mention has yet been made of Porphyry or other varieties 

 of granite rocks ; but it may be concisely stated that there are in- 

 stances of slate rocks converted to porphyry, of porphyry passing 

 to granite, and of porphyry which has undergone a crystalline 

 tendency. Here is a rude octohedron of porphyry from near 

 Harvey's Range. At Port Stephens I visited a Cone Hill, on 

 the summit of which there is a most remarkable assemblage of 

 prismatic columns, of almost equal interest with those described 

 by Humboldt as occurring in the Andes. 



Many of the Porphyries in New South Wales, where they 

 have been silicated, exhibit beautiful double hexahedral prisms, a 

 variety, no doubt, due to transmutation, and which is generally 

 considered to belong to the Devonian epoch of Europe. Such 

 porphyry occurs on the Hunter, and at Arthursleigh, near the 

 Wollondilly, in Argyle. 



It would take up too much time to dwell on the jasperised 

 rocks, which are another result of granitic transmutation. I can 

 only say that they are extremely common in parts of this colony, 

 and also in the northern part of New Holland generally, I have 

 examined huge examples of this change not far from the granite 

 of the Peel River and Hanging Rock districts ; and I have little 

 doubt that the jaspers so common in certain beds of our coal- 

 fields have been derived from the destruction and abrasion, and 

 driftings and deposition of the fractured rocks of an earlier age, 

 allied to that to which the example above quoted clearly belongs. 



Here, again, we are on the limits of equal change produced 

 by Granite and Trap. 



The trappean rocks include basalt, dolerite, greenstone, 

 diorite, and various others, in which the felspar is hydrated and 

 allied to lime felspar. In the granitic rocks, the felspar is an 

 orfchoclase or potash felspar. 



Trap rocks are assumed to have been formed under water, and 

 to have been subjected to great pressure ; but when they come 

 near to day, they become vesicular, puffing off their steam or 



