BY THE REV. W. B. CLARKE, U.A., F.G.S., 271 



Isle of Elba, where that rich habitat of iron is in close proximity 

 with granite, and in this colony about the Dromedary Mountain 

 and from it to Maneroo. 



In contact with granite rocks, coal is often converted into 

 Anthracite and Graphite. 



In New South Wales I have often found Pegmatite or 

 graphic granite at the points of intrusion of ordinary granite, 

 and in some instances corroded. In certain cases in some 

 countries, corroded pegmatites are very metalliferous. Again, 

 granites are frequently found in a decomposing state, called 

 rotten granite. In such cases the rotten granite is traversed 

 oftentimes by porphyritic elvans or by quartz veins. Such may 

 be seen on the descent from Bowenfells to the river Cox, on the 

 Bat hurst line ; it is an instance of transmutation effected, 

 perhaps, by silicated vapours which have resulted in quartz 

 veins : and it was in one of those very spots I first found Austra- 

 lian gold in 1841. 



I must anticipate here the mention of a fact connected with 

 granite, which is curious, that rock which is enveloped in or 

 entangled with granite, is very seldom if ever prismatised or 

 altered into columns the columnar structure being extremely 

 common in rocks that are in contact with trap. The conclusion 

 to be drawn from such a fact is, that the granite could not be as 

 hot as the trap, and therefore the plasticity of granite is not due 

 to simple fusion. 



On the other hand, where granite has been itself enveloped in 

 igneous matter lava for instance, it undergoes a change. 



Witness this specimen from an extinct volcano in Auvergne. 



Granite produces a singular change on certain arenaceous 

 rocks, as in this fragment broken off at the junction of a granitic 

 intrusion with " green sand." It is silicified. 



Silicincation is a very common product of the contact of 

 granite with calcareous rocks. Limestones thus affected exhibit 

 their fossils frequently silicified, and the unsilicified limestone is 

 changed to a saccharoidal marble, the colours passing away, and 

 the marble becoming white. 



Occasionally, however, similar changes in limestone have 

 been produced without contact with granite ; and the transmn- 



