140 Mineralogy and Geology of a part of Nova Scotia. 



imperfectly polished fragments among the rolled masses on 

 the shore. A vein of magnetic oxide of iron about a foot 

 wide was also observed entering the superincumbent trap. 



But the substance for whicli this island has long been 

 known by the inhabitants of the country is amethyst ; which, 

 occurring plentifully in crystals of fascmating beauty, draws 

 hither the passing traveller, who seldom departs without 

 something ornamental to his parlor shelf, or useful to science. 



Pursuing the northern shore of the Basin of Mines, east- 

 wardly, the next place deserving of notice is the vicinity of 

 the Two Islands, about six miles from Partridge Island. The 

 intermediate coast, being composed of rocks of a different 

 character from those which it is our object at present to de- 

 scribe, we shall leave, to notice it more particularly when we 

 treat of that formation. 



The Two Islands consist of amygdaloid and columnar 

 greenstone rising on all sides abruptly from the sea, and be- 

 ing accessible at their bases only at low water will not afford 

 the visitor many interesting specimens. On the main land 

 near Swan's Creek, and opposite to these islands, he will be 

 favored with a locality of uncommon interest. At this place 

 also we have a second, and perhaps better developed exam- 

 ple of the conversion of shale, red sandstone, and compact 

 trap, first into a coarse breccia, consisting of loosely united 

 masses of these rocks, then into a more compact breccia, 

 consisting of similar masses more closely united, though 

 distinguishable from each other, and finally, by consecu- 

 tive gradations, into a genuine, well characterized amyg- 

 daloid, in which the most critical eye would fail to distinguish 

 separately its component ingredients. We have in our pos- 

 session specimens from this place, which illustrate perfectly 

 the changes of which we speak, and which present these 

 three rocks tending to the production of amygdaloid. The 

 color of this amygdaloid is obviously governed by the rela- 

 tive quantity of the ingredients composing it ; for if the sand- 

 stone and red slate predominate, the color is then nearly of a 

 brick red, as the appearance of the rock itself abundantly 

 proves ; but when it assumes a greenish or greyish black co- 

 lor, we infer that the slate and sandstone form a compara- 

 tively small proportion of the mass. 



Having thus adverted to the character of this rock in par- 

 ticular, we shall notice more generally the appearance of the 



