564 



On its eastern side the igneous rock is bordered by a dark- 

 coloured graphitic slate, which has been much broken, healed, 

 and seamed along the lines of fracture. Nearby, this slate 

 has been pushed out of the line of strike, from a north and 

 south to an east and west direction. This igneous occurrence 

 is the only one observed on the northern side of the Cathedral- 

 rock Creek. 



Group (b) ON RIDGE AND SLOPES ON SOUTHERN SIDE OF THE 



CATHEDRAL-ROCK CREEK. 



Nos. 3, Jf., and 5. — The outcrops thus numbered bear 

 certain relations to each other, and collectively form the 

 largest development of igneous rock in the neighbourhood. 

 It is an irregularly-shaped mass, occupying the summit and 

 slopes of the ridge nearest to the mount on the southern side 

 of the Cathedral-rock Creek. No. 3 (forming the portion 

 nearest the mount) is subcircular in outline and measures 90 

 yards by 80 yards. The limestones bordering the igneous 

 mass appear to have been controlled by the latter, as they 

 follow a circumlinear strike marginal to the igneous intrusion. 



Following the top of the ridge, in an easterly direction, 

 the impure limestones and calcareous slates occupy the ground 

 for about 30 yards, and then another important outcrop of 

 basic igneous rock is met with, forming a part of No. If. 

 At first sight Nos. 3 and If might appear as independent out- 

 crops, but on a closer examination it is seen that they are 

 connected by a relatively narrow neck, just over the crest, 

 on the southern side of the ridge. Near the summit of the 

 ridge the No. If dyke has a width of about 57 yards, but 

 narrows as it passes down the slope on the south-western 

 side and junctions with" the No. 3 outcrop. The calcareous 

 beds which separate the two igneous intrusions at the summit 

 of the ridge are squeezed into the form of a triangular wedge 

 between the two arms of the igneous rock. As No. Jf passes 

 down the north-eastern slopes of the ridge it increases in 

 width to 88 yards and makes a spur that ends on the terrace 

 formed by the right bank of the creek. 



The lithological features of this igneous zone (Nos. 3 and 

 Jf) are particularly interesting on account of the variation 

 in the texture and form of the rock at different points. Near 

 the periphery the rock is remarkably fine-grained and, to the 

 naked eye, might be cryp to-crystalline, while in the more 

 central portions it is conspicuously crystalline and even 

 gabbroid in its appearance. About two-thirds of the distance 

 down the spur forming the No. If. outcrop there is a rounded 

 knoll of porphyrite, which is enclosed in the very heart of the 

 basic dyke. The porphyrite is rendered partially fissile by 



