GRANITES OF CATHEDRAL ROCKS. 
35 
around is covered with large loose fragments of felspar. At the foot of G 3 , 1500 
feet above sea-level, the felspars in the rock are even larger than those on the 
summit, and a dark dyke (714) 
(see p. 131) with phenocrysts of 
hornblende up to two inches long 
is exposed a few feet above the 
ice. In addition, below’ this “ dark 
dyke,” thei’e is a green band of a 
fine-grained rock (732) about five ^ 
feet thick. The dark dyke pro- Jj 
duces a dark patch on the hillside, £ 
which, owing to the contrast, can § 
be seen at least 10 miles away. 
On the opposite side of the glacier, 
above d 3 , there are three or four 
similar patches which, though 
larger, are probably due to a 
similar occurrence of dykes. 
The Cathedral Rocks. 
These rocks already referred to 
(see p. 30) form a very imposing m . 
triple headland on the south side 8 
of the Ferrar Glacier, and are as -s 
important as they are picturesque, 
for here, there seems no doubt, is ° 
contained the whole history of the 
Royal Society Range. At the base, 
as already stated, is banded gneiss. 
Above it, and divided sharply from 
it, is the granite, which must be 
about 4000 feet thick. Above the 
granite is a sheet of dolerite, which 
o 
is rendered conspicuous by its 
weathering back faster than the 
granite and leaving a prominent 
ledge. Upon the. dark dolerite- 
sheet is a yellow cap, presumably of sandstone, which forms the summits of all 
three headlands (Fig. 17). (See Sections I and II, Plate VII.) 
