348 C. A. S13SSMILCH AND W. G. STONE. 



blende; the relative proportion of these two minerals is 

 very variable, in some specimens the augite preponderates 

 to the exclusion of the hornblende, while in other speci- 

 mens the reverse is the case. This type occurs as more 

 or less rounded inclusions in the non-porphyritic type, and 

 very irregularly distributed through it; the inclusions 

 themselves are very variable in size ranging from an inch 

 up to several feet in diameter. The junctions between the 

 two types are always quite sharp. 



This rock weathers very readily and gives few good out- 

 crops, and little would therefore have been known of it, 

 had it not been cut away in making the foundations for the 

 Cave House, and in making road cuttings. These operations 

 have not exposed either wall of the dyke. 



At the other good outcrop mentioned (the place marked 

 A on the map) instead of one large dyke, there are two 

 small dykes, which are exposed in the face of a waterfall 

 in the channel of one of the tributaries of McEwan's Creek. 

 One of these dykes contains the non-porphyritic type of 

 andesite only, and is ten feet thick, the other contains the 

 porphyritic type only and is fifteen feet thick, (see Fig. 2). 



A C B C 



Fig. 2 — Sketch Section at A on Map (Plate LV) showing 

 andesite dykes intruding radiolarian cherts. A — Andesite-porphy- 

 ritic type. B — Andesite-non-porphyritic type. C — Radiolarian 

 cherts. 



