34 DISCUSSION ON NOTES ON THE MOUNT LYELL DISTRICT. 



hope that when -we have fuller knowledge of the movements 

 of the crust we shall find a clear explanation of their cause." 

 Until that time arrives we must be content provisionally with 

 that hypothesis which seems to account most reasonably with 

 the greater number of known facts. The proof of a more 

 perfect theory has not yet been made evident. 



Me. Stephens, F.G.S., said that the author of the paper 

 under consideration had evidently paid much attention to the 

 geological formations of a portion of the "Western Country, 

 but, in dealing with the question of the history of the 

 mountain systems and the general physical structure of 

 Tasmania as a whole, he appeared to have relied too much 

 on the information supplied by maps, which is necessarily 

 very imperfect. That the chief agency at work in producing 

 those undulations in the primary rocks which had brought 

 into existence many of the mountain ranges and valleys 

 of Tasmania might be traced to secular cooling and contrac- 

 tion of the earth's crust there could be little doubt, and the 

 mountain systems of later date owed their origin indirectly 

 to the same cause, though the valleys had, for the most part, 

 been scored out by the ordinary processes of nature working 

 on the surface of the country. " In addition to what had 

 been said in opposition to Mr. Power's water pressure and 

 wave theory, it might be pointed out that until portions of 

 the crust had been raised there was no deep sea, and there- 

 fore all that the weight of the water could do, if it had any 

 effect at all, would be to moderate the downward pressure of 

 neighbouring mountain ranges, which are always in a condi- 

 tion of continuous resistance to the forces which had elevated 

 them. With reference to Mr. Power's remarks on the con- 

 glomerates of the West Coast, there could be no doubt that, 

 as he suggests, some of the gold in the alluvial deposits has 

 been derived from conglomerate formed from the waste 

 of auriferous rocks. On the other hand it has to be borne 

 in mind that, while there are many conglomerates inter- 

 stratified with the primary rocks, and likely to contain gold 

 in cases in which the cemented materials have been derived 

 from auriferous veinstones, there are other conglomerates of 

 more recent date which have been derived from bands of 

 quartz rock, quartzite, and associated schists, such as occur 

 in great force at Mount Arrowsmith, Rocky Cape, and else- 

 where, in which no gold occurs to any appreciable extent. 



Mr. A. Montgomery, M.A., Government Geologist of 

 Tasmania, regretted the absence of Mr. Power, as he would 

 have liked to have had from him further explanation of the 

 new theories advanced. The subject matter of the paper had 

 a very wide scope, comprising two new theories, one of the 

 formation of mountain chains, and a second of the origin of 

 lodes in general, and of the Mount Lyell lode in particular. 



