17l3 THE CANADIAN NATURALIST. [Vol. X. 



with the strike of the amygdaloid beds. I had no opportunity 

 of observing, in most instances, how far they extend inland ; but 

 in two cases they are distinctly terminated at a very short dis- 

 tance from the shore — the serrated and indented aspect of which 

 is doubtless due to the resisting qualities of the harder rock 

 acting like the enamel on a tooth, ^Yith perhaps two exceptions 

 which I shall proceed to notice, the crystalline trap masses cannot 

 bt; regarded as intrusive, as supposed by Sir William Lo^an, at 

 least not at this place. The impression conveyed to my mind 

 by the whole phenomenon — if I may be allowed to theorize — 

 wa.> that the materials of the amygdaloid had been first ejected 

 in the form of volcanic mud or allies, and thereafter overflowed 

 by a fluid current of molten matter of nearly the same chemical 

 constitution, but very diff"erent mechanical properties, filling up 

 cracks, fissures and depressions in the original surface, and there- 

 after denuded, leaving only such portions as we now find in the 

 form I have attempted to describe. 



One very notable exception (or perhaps two) to this arrange- 

 ment has to be remarked. I refer to the existence of a iireat 

 dyke of the same hard crystalline trap, undoubtedly penetrating 

 the amygdaloid in a nearly vertical direction to an indefinite 

 depth, and also extending indefinitely inland to the west, parallel 

 to the strike, in a perfectly straight line, and preserving a uniform 

 thickness of about sixty teet. It is of a transversely horizontal 

 columnar or rather sub-columnar structure, the columns lying 

 truly at right angles to the direction of the dyke, and dipping 

 south at an angle of 7*^', or exactly at right angles to its down- 

 ward direction, which deviates to this extent from the perpen- 

 dicular. The dyke juts out boldly into the deep waters of St. 

 Tgnace Bay about the ceatre of the location ; and, no doubt, 

 together with the hardness of the adjacent masses of crystalline 

 trap, has been the cause of the existence of the great pro- 

 jecting cape of am3'gdaloid to the north, by protecting it from 

 the wasting action of the waves. It is flanked on either side by 

 veins of a remarkably promising character for silver and copper ; 

 the vein-stone, which is entirely diff"Lrent from the inclosing 

 rocks, although containing fragments of them, being composed of 

 quartz, calcareous spar, baryta, laumontite, prehnite and much 

 chloritic matter, together with garnets, native silver in very fine 

 loose particles, and vitreous copper ore. It was to these veins, 

 after discovering them, that I chiefly directed my attention in 



