BY SYDNEY B. J. SKERTCHLY. XVll 



elusion that the interpretation of the geological structure of 

 the Chillagoe district as heretofore adopted by ]\Ir. R. L. Jack 

 and myself must be profoundly modified. Neither of us had had 

 opportimities for more than making rather hurried traverses, our 

 official duties necessitated our time being mainly devoted to the 

 more commercial problems of the actual mines. Hence, it was 

 not until I had time and opportunity to study the limestone, that. 

 the true significance became apparent. We had both naturally 

 concluded that as the limestone appeared to lie along the general 

 strike of the rocks, and as the slates, etc., cropped out between the 

 various limestone blufis, and finally, as the limestone is seamed 

 with more or less vertical division planes, that there were several 

 beds of limestone intercalated in the slate and sandstone series, 

 that any peculiarities in the lie of the limestone might be 

 accounted for by faulting. 



^^'ith this impression still on my mind, I started to map a 

 great part of the country in detail, and found that our old theory 

 was not l)orne out by facts, and that instead of the Limestone being 

 one or more beds of intercalated in the slaty rocks, it was really 

 quite unconformable to them. The Chillagoe Limestone, in fact, 

 lies as a much denuded cake extending over the upturned edges 

 of the Herberton rocks, and losing itself on, and partially in, the 

 granite which has disturbed and altered it. What we thought 

 to be l)edding-planes are really a rough system of cleavage 

 planes, which like those in the underlying rocks owe their origin 

 to the strains set up by the intruding granite. No system of 

 faults, however complex coiild accoiint for the lie of the lime- 

 stone, and in many places both round ]\lungana and thence to. 

 Calcifer, the last relics of the limestone can be seen fading out> 

 as it were, into isolated patches a few inches thick lying upon the 

 Herberton rocks. 



So far from the limestone being nearly vertical, it really lies 

 in a series of low folds. Here and there, as in the caves at 

 Mungana, lines of broken encrinites and other organisms can be 

 seen still occupying very nearly their original horizontal position. 



In many places both along the Northern and Southern 

 boundaries of the granite the limestone is altered into a very 

 coarse crystaline calcite, individual crystals being often several 



