9 



them. Some veins of a similar substance are vesicular. I believe, however, that tliis appear- 

 ance has resulted sole^y from the iron contained in these portions of the rock. Close to 

 this is a band, about 8 feet in breadth, of vertical laminae half decomposed and with crus- 

 tated projecting edges. Internally it is composed of crumbling felspar having minute scales 

 of mica scattered through it. Towards the surface the hue is rusty and some deep black 

 stains occur throughout. 



Near the point the rock exhibits great variety in its composition even within a small 

 compass. One specimen has a greenish grey sacchariod felspathic base in which crystals of 

 quartz and nesfs of mica are sparingly disseminated. Another is somewhat similar, but the 

 base is a dark brownish grey. In others whitish felspar and black mica and hornblende 

 are united in different proportions, equal and well separated, or more finely granalated 

 and mingled, so as, when the mica is absent, to approach to the character of a syenitic 

 greenstone. 



Among the other interesting examples of varying structure and composition at the Point 

 thcre are some solid blocks of a rudely globular shape , with the rock in the spaces bet ween in 

 foliae from l-6th to l-8th of an inch thick. Adjoining these are some blocks which, within 

 a circuit of a few feet, change in their appearance and composition, passing from a black 

 doleritic rock into a well crystallized compound of hornblende and felspar (syenitic dole- 

 rite) in which the former is greatly in excess, — into a similar rock in which the felspar 

 greatly increases and which at one place is intersected by a rhomboidal network formed by 

 felspathic veins crossing each other, — and, lastly, into a whitish grey rock similar 

 to that around the globes before noticed. The crystallization between the opposing convex 

 sides of adjoining blocks exhibits yet another andstill more strongly marked variety, becom- 

 ing abruptly very coarse, so that some of the specimens which I took from the line of junc- 

 tion have, on one side, either a granite as minute in its granulation as fine sandstone, 

 or a compact dolerite, and, on the other, crystals of felspar and scales of mica of an un- 

 usually large size. 



A little beyond the SE. angle there is a band of semidecomposcd rock about 2 feet 

 broad consisting of small globular and cuboidal bosses, from 3 to 6 inches in diameter, of a 

 very fine grained granite or eurite imbedded in, and protruding from, yellowish white clay. 

 The former are composed of minute micaceous and hornblendic grains thickly disseminated in 

 a base of granular quartz and felspar. It so strikingly resembles fine ground pepper, especial- 

 ly after decomposition has commenced, that it may be called pepper granite. The latter has 

 originally been in great measure felspathic. 



At the SE. Point the slight superficial depressions marking divisional planes, the prin- 

 cipal fissures and chasms, and the longer sides of separate ledges are all in NE.-SW. 

 lines, or lines not deviating far from these directions. The first have given rise to the 

 two last. The cohesion of the rock at the divisional plane, originally least, is further 

 weakened by partial decomposition along that line. The alternations of témperature from 

 exposure to the rays of a burning sun succeeded by immersion under the waves, and the 

 removal of support on either side by the mechanical action of the sea, cause the rock to 

 split along the plane, and thus a fissure is formed. A ledge or band between two fis- 

 22 st0 deel. 1847. B. 



