
oD ee ae eee. ee eee 

CRETACEOUS AND TERTIARY—THREE BUTTES. 125 
out a quantity of gravel m one of the small brooks, but without being 
able to detect the presence of any valuable metal; a small quantity of 
magnetic iron and garnet sand from the northern drift, being the only 
result. 
307. Nearest the trappean mass, and lowest in the series on the Hast 
Butte, occur beds of hardened sandstone, not of great thickness ; on these 
rests a considerable thickness of hard, blackish, fissile shale, in which no 
characteristic fossils were found, but which from the sections afterwards 
examined near the West Butte, are no doubt referable to the fourth 
division of thé Cretaceous, and represent the sombre clays, and clay- 
shales, so frequently observed further east. Above this, is a rather exten- 
sive sandstone formation, much of which is regularly bedded, but which 
in some places is nodular, and gives rise in the vallies which cut through 
it to castellated, step-like, and fluted rocks of picturesque appearance. 
Next in order are the clays, sandstones and arenaceous Clays, character- 
ised by Ostrea, &c., already described as constituting the substratum of 
the plain. 
308. The igneous material, composing the higher peaks and central 
masses of the mountains, though very hard and’ compact, is seldom seen 
actually in situ, the solid rock being concealed under a great depth of its 
own fragments. These are very irregular in form, but generally angular, 
and .bounded by plane faces; they vary in size from a few inches to 
about two feet in greatest diameter, and render the upper slopes utterly 
barren. The rock is very uniform in appearance and composition. It 
is usually a Rhyolitic Trachyte-porphyry ; but, by the introduction of a 
smal! quantity of hornblende, sometimes passes, without otherwise much 
changing its appearance, into a material;which may be called a Sanidine- 
trachyte. The matrix is pale greenish-grey, porcellanous, but not 
perfectly homogeneous, and encloses crystals of sanidine felspar, which 
vary from those barely visible, to others which attain an average size of 
about 3 millimétres. Quartz is present as a constituent in small quantity, 
forming minute granular aggregations; and specks of pyrites are generally 
to be seen. The hornblende, when it occurs, is found generally in very 
small crystals between those of the sanidine, but sometimes forms 
bunches an inch or two in diameter, which appear as darker spots on the 
surface of the rock. 
309 The highest peak of the West Butte, is at its eastern side, and 
is a large blunt-topped mountain, which to the east presents perpendi- 
cular rocky cliffs, West and north of this summit, several important 
