and Igneoiis Rocks of Ensay. 121 



It mio-ht be thought that such mineral alterations as those 

 I allude to in the argillites might be produced by the perco- 

 lation downwards of surface waters. No doubt the action 

 of such mineralised waters must not be lost sight of in any 

 hypothesis which proposes to account for the present condi- 

 tion of rocks at the earth's surface. 



But an explanation relying upon such solutions as a 

 principal cause of even the lesser metamorphic changes will 

 not account for the connection there is between the molecular 

 regeneration of the sediments and the disturbance, disloca- 

 tion, and compression to which they have been subjected. 

 Nor will an explanation which relies upon the action of 

 heated mineral waters from below be more satisfactory, and 

 for the same reasons. The structural changes which the 

 mineralised beds show point to other causes, which must be 

 considered. It seems to me that an hypothesis to be satis- 

 factory, in conforming to observed facts, must not overlook 

 the forces brought into play during the vast tilting, folding, 

 and especially crushing, to which, in Palaeozoic ages, the 

 Silurian sediments were affected : that is to say, during 

 those periods of time when the mineralisation of the strata 

 was effected. 



It is quite certain that in Gippsland, at the close of the 

 Silurian age, gigantic movements of the earth's crust folded 

 the sediments together, and crushed them close. This 

 certainly produced an amount of motion in the rocks which, 

 within reasonable limits, it is difficult to overstate ; and the 

 question then is : What did this movement result in beyond 

 the physical effects which can be seen still impressed upon 

 the stubborn but bent and contorted strata ? 



In following out this train of thought one is easily led to 

 the reply, that those vast movements must have generated 

 an amount of heat proportioned to their own extent. 



It must be borne in mind that the mere pressure of for- 

 mations lying upon each other does not seem capable of 

 producing such changes as those I refer to in the argillites 

 of North Gippsland, even when many thousands of feet of 

 beds are horizontally upon each other. But it is different 

 where pressure causes the forcible movement of the rock 

 particles among themselves, and especially the folding of the 

 strata. It is under such circumstances that pressure can 

 generate metamorphic action, and especially when the sedi- 

 ments acted upon are still permeated by the waters of the- 

 oceans in which thev were laid down. 



