241 



ON A REMARKABLE EXAMPLE OF CONTORTED SLATE. 



By Archibald Liversidge, Professor of G-eology and 

 Mineralogy in the University of Sydney. 



[Read before the Royal Society o^ N.S.W., 6 Decemher, 1876.] 



THe specimen of more or less imperfect slate which I now have 

 the pleasure to lay before the Society is, I think, a most remark- 

 able example of true contortion, accompanied by slaty cleavage, 

 but contortion on such an extrem^ely small scale that it in certain 

 aspects appears to resemble the well-known cone-in-cone structure 

 seen in coal and many rocks. 



The specimen was obtained by Mr. Eielder from the Peelwood 

 Copper Mine, near Tuena. Mr. Fielder succeeded in detaching 

 this, most interesting and beautiful example from a projecting 

 point of weathered rock, but only after the expenditure of much 

 time and trouble, for the slaty rock was far too tough, and also 

 too fissile, ii0 admit of its being broken off in large blocks by 

 blows from a hammer or pick, so he had to saw it off — a very 

 tedious and laborious operation. 



It will be equally, observable in the specimen and the photo- 

 graphs which I lay before you, that some of the plications are not 

 more than, even if so much as, an eighth of an inch across, whilst 

 the widest of them do not exceed two inches, and the depth of the 

 largest cleavage plane in the specimen barely reaches three 

 inches ; its extent in the direction of from before backward I 

 have no means of telling, as the specimen sawn off had a thick- 

 ness of but about two inches. The dark lines Z, m, n, and u, v, in 

 plate II, represent fractures in the specimen, and their plications 

 beautifully indicate the cleavage planes to which they are 

 parallel. Whether the cleavage planes extend over any length 

 of country I do not know, as I have not visited the locality 

 whence the block was brought, neither have I been able to 

 obtain particulars on this point. The contortion is probably of 

 quite a local character, as it does not appear to have been noticed 

 elsewhere in the district. 



The rock or slate has the appearance of the grey killas of 

 Devon and Cornwall ; it is in all probability of Devonian age. 



