136 SCIENCE PROGRESS 



stratified beds; but as had been maintained by Mr. William 

 Bradford, of Ballarat, they cross the bedding planes irregularly. 

 They are secondary in origin, and, though they are limited to 

 particular bands of slates, they do not occupy uniform positions 

 in these bands. 



Microscopic examination of the indicators, moreover, show 

 that they are not layers of pyrites. This view was based on 

 the fact that they appear, in the upper levels of the mines, as 

 thin iron-stained bands ; and the iron was thought to be derived 

 from decomposed pyrites. The typical indicators are seams 

 of chlorite ; one of them, the Pencil Mark, is a thin band, 

 rendered black by the abundance of fine needles of rutile. 



The indicators are seams of secondary minerals, generally 

 chlorites, developed along slip-bands traversing the slates. 1 



1 Since this article was written a somewhat longer account of the Indicators, 

 with some illustrations of their microscopic structure, has been published in The 

 Mining Journal, vol. Ixxix. p. 78. 



