in South Australia. 175 



Such a disturbance must have had some particular cause to 

 make it exert itself in so uniform a manner. Thus, there is 

 upheaval of the slate, crystallisation of the same, and upheaval of 

 the hills in nearly the same direction. We are not at present 

 aware of the mode in which hills are upraised, but the general 

 supposition is, that fire causes the disturbance : and if fire was so 

 long an active and yet so partial an agent, as to cause the same 

 disturbance, at the same places, at different times, it can easily be 

 imagined to have been equally partial in affecting the slate, 

 though the manner in which it did so is not patent. Or to 

 make it plainer, if it upheaved parallel and narrow chains of 

 hills, leaving sometimes wide valleys between, it can be easily 

 understood to have altered some part of the slate and sjoared 

 others. If these facts shoidd hereafter be looked into, the idea 

 that mountains are upheaved through igneous agency, will be- 

 come something more than a mere supposition. 



I have one more question to settle, that is the age of these 

 rocks. They are very (geologically) ancient, but enclose no 

 fossils. Had they done so formerly such remains would, of 

 course, have been obliterated by the metamorphic action. They 

 are probably of either the Cambrian or Silurian formation, but 

 this is mere guesswork, supported by little more than resem- 

 blances hi mineral character, &c. That they have existed for 

 ages in their present position cannot be doubted, for it takes no 

 small time to decompose hard slaty rock into a surface soil, 

 sometimes many feet deep. Veins of segregation too, as I have 

 observed, are common. Some of them are of quartz, and have 

 doubtless been formed in many cases by silica filtering into 

 crevices already made in the metamorphic rock. This is a fact 

 where observation is much wanted, as it is not at the present 

 moment in any way clear, to what we are to attribute the quartz 

 veins which occur so commonly in rocks. In the instances I 

 am mentioning it is difficult to attribute them to heat, and 

 yet though filtration is the only resource to explain them, 

 the peculiar manner in which it is exercised in these 

 cases is but very imperfectly understood. The Dolo- 

 mites I have mentioned have doubtless been formed in 

 the wet way, by the re-action upon each other of carbonates 

 of lime and magnesia. The same may be said of the steatite. 

 The altered rock where the crystallization has been perfect 

 is a light granular stone, with white flour-like feldspar 

 disseminated through it. It is sometimes of a pure white colour, 

 sometimes a pinkish yellow, and .again a deep red and highly 

 ferruginous. The specific gravity ranges from 2.4 to 2.86. 



