Middle and Upper Palaeozoic Rocks . 41 
This general slope is not merely due to denudation — though 
that agency has exercised upon it a certain modifying effect, and 
has also produced great surface changes in eroding valleys, &c. — 
hut chiefly to an actual dip in the ancient land surface of the 
period to which the porphyries belong, as it is found that the 
Lower Pakeozoic rock-foundation on which they rest has a similar 
slope ; and that, while at the northern portion of the plateau the 
Lower Pakeozoic rocks constitute from 2,000 to 2,500 feet of 
its base, and the porphyries form the remainder, the former pass 
out of sight beneath the level of the rivers near Buchan, where 
the latter still reach an altitude of 2,000 feet above the sea. 
The bulk of the rocks consists of felstone-porphyries, felstone- 
ash, and agglomerates : the lower portions of the series approach 
more nearly to the quartz-porphyries in character, and are more 
compact and porphyritic than the upper 2,000 feet, which exhibit 
clearly a fragmentary character. The fragmentary portions vary 
from microscopic dust to several feet in diameter, are usually 
angular, more rarely slightly rounded, and consists of fclstoncs 
and quartz-porphyries of various kinds embedded in a felstono 
base. The occurrence of a fragment of well-marked granite 
among the varieties of felstoues and quartz-porphyries is also noted 
by Mr. Howitt, who adds, however, that he has not observed 
fragments of sedimentary rocks in these agglomerates. In places, 
particularly in the Little River, a branch of the Snowy River, a 
distinct bedded or stratified appearance is noticeable both in the 
fragmentary and in the more compact and porphyritic felstoues, 
though they do not present auy evidence of the action of water in 
.sorting and arranging the beds. (Figs. 8 and 9.) 
Fia. 8 .— Little River. 
Dip of beds, N. 15°. 
