98 



upon which it depends for its durability, as it probably 

 does upon the different degrees of oxidization of the Iron 

 contained in it for the shades of colour. Killas and all the 

 schistose rocks in Cornwall are only different varieties of 

 this substance, depending upon the Talc, Quartz, &c, be- 

 ing somewhat varied in quantity and texture ; which varia- 

 tion may easily be supposed innumerable, but which may 

 without much practice be recognized, although the word 

 Killas seems to have caused some confusion. 



The lowest figure is Slate from Ingleton*, in Yorkshire j 

 and, like the Irish, Welsh, and Scotch Slates, often have 

 cubes of Pyrites in them. 



The present specimen is one of that sort, and has a newly- 

 noticed substance on two sides of the Pyrites. We have 

 mentioned it to many friends, but can neither gain intelli- 

 gence about it, nor learn whether it is to be had in better 

 specimens. This is somewhat like Asbestus, the fibres 

 being at right angles with the Pyrites on two sides only. 



The left hand is a specimen from Westmoreland. 



* This place is famous for dendritical Pyrites on the Slate, forming as it 

 vrere golden trees (see right hand figure)- 



