mo 



Outlines of the Mineralogy and Geologjf 



of a bluish grey colour and efferv 



with 



acids 5 by exposure fo the atmosphere the surface becomes disia 



rated and earthy ; it is found at Charlestown. We hi 



no metals in Argillite, but the Sulnhuret of Iron 



ob 



served 

 by its 



of rust 



decomposition^ frequently covers the rock with a coating 



HI* PRIMITIVE I'RAP. 



I. The word Trap is applied to those rocks, which contain 

 Hornblende as their principal ingredient. They are divided into 

 two sections, viz. those composed principally of Hornblende, and 



those composed of Hornblende and Feldspar; the latter constitutes 

 the rock, called 



GREENSTONE, 



of which several varieties occur. 



i. Common Greenstone, 



II. This is a granular aggregate of Hornblende and Feldspar. 

 The general colour is greenish, greyish, or greyish black, of va- 

 rious intensity ; the two ingredients are often united in nearly 

 equal proportions, though sometimes the Feldspar, but general- 

 ly the Hornblende predominates. 



the Feldspar are reddish, and greenish 



III. The colours of 

 hite ; the latter is the r 



and is prod 



sometimes 

 of the 



by Epidote and sometimes by Hornblende. T „, 



Feldspar varies from quite compact to more or less perfectly foli 

 ated, and fine splintery ; its lustre is shinin 



• Bs waxy. The colours of the Hornblende are blackish and 



dull and 



greyish 

 glistening lustre 



fracture 



even 



^ 



liy foliated and with 



t 



