Mineralogy and Geology of a part of Nova Scotia. 1 43 



or less proportion, as an essential ingredient of the rock. 

 The breccia, or trap tuff, which is a constant attendant of 

 the amygdaloid produced by the union of the sandstone, 

 &c. and which seems as an intermediate form necessary to 

 the constitution of the latter, is here observed, as in all oth- 

 er places of similar character, superincumbent on the amyg- 

 daloid. 



The Island most noted among these is that, which standing 

 in advance of the others, is a conspicuous object to meet the 

 eye of the mariner, in his progress up the Basin. It is com^- 

 posed of amorphous or indistinctly columnar trap, which rest- 

 ing on a softer basis of amygdaloid, presents, from the un- 

 dermining action of the surges, the curious phenomena of 

 a leaning tower, and, casting a dark, broad shade beneath 

 it, seems as if ready to tumble into the sea from the over- 

 hanging weight of its summit. 



On the southern front of Tower Hill is a precipice of 

 about one hundred feet high, constituted of red sandstone 

 containing red shale, and having for its summit rock, a low 

 ridge of amorphous trap, resting immediately upon the sand- 

 stone, without the intervention of any other rock. It pre- 

 sents vertical veins of quartz, sometimes crystallized, but is 

 void of the zeolites ; nor were we able, during our visit at 

 this place, to discover a single crystal belonging to that fam» 

 ily of minerals. 



This is the last place on the shore of this Basin at which 

 trap rocks are known to occur. Still farther east, the sand- 

 stone interstratified with shale, uniformly and uninterrupted- 

 ly prevails. This spot may therefore be regarded as the ex- 

 treme eastern limit of the whole trap formation of Nova 

 Scotia, and having for its opposite extremity Briar's Island, 

 which, as may be seen on the map, is not less than one hun- 

 dred and fifty miles distant, comprising within the intervening 

 space, a field alike extensive for mineralogical and geological 

 research, and replete with numerous objects of natural his- 

 tory. 



Having finished our account of the trap rocks forming the 

 North Mountains and their outskirts, which comprise a com- 

 plete description of that formation, with the more important 

 and curious mineral productions which they include, and hav- 

 ing suggested, what appears to us the most obvious theory of 

 their origin, which, derived from remarkable peculiarities 

 of color, structure, and other appearances of contiguous 



