EXTENT OF DOLERITE-FORMATION. 
53 
dolerites to maintain uniform horizons for so great a distance, and to remain always 
separated by the same thickness of sandstone. The sandstone between the sills is 
always about 500 feet thick. 
The Former Extension. 
On consideration of the facts stated above, it will be seen that wherever a 
dark rock was encountered it proved to be dolerite ; further, all the abundant dark 
fragments in the moraines belonged to that kind of rock. Dolerite has been shown to 
cap the highest sandstone seen, and to be intrusive into it on each side of the upper 
Ferrar Glacier. Some mountains are entirely composed of dolerite, and others, such as 
the Beacon Heights or Knob Head Mountain, have mere caps of that rock, which may 
be remains of a once con- 
tinuous sheet. At the 
Cathedral Bocks dolerite 
must rest upon granite, 
and apparently at one time 
have been continuous with 
the sheet which caps the 
granite in the Kukri Hills. 
Further, the Royal Society 
Range, which is a faulted 
crust-block * and is 
higher than any of the 
surrounding country, has 
strongly developed 
plateau -features (Fig. 9, 
p. 23) ; the rock which 
forms the highest peaks 
is dark and therefore pro- 
bably dolerite. If this be so, we may be sure that both dolerite and the Beacon 
Sandstone Formation extend quite 50 miles in an east-and-west direction. 
Next, dolerite caps the Beacon Sandstone at the Inland Forts, and the hills 
for at least 10 miles north are capped by rock which cannot be other than dolerite. 
The contrast in colour between cap and sandstone is always so strong that this 
inference could be made even without regard to the evidence of abrupt changes 
in the hill-outlines at the junctions. For similar reasons there can be no doubt 
that the dolerite still caps the sandstone-hills, which extend 10 miles to the south 
of the main Ferrar Glacier (Fig. 28). These facts render it extremely probable that the 
Cathedral Rocks Kukri Hills 
Fig. 27. — The dark band in the Kukki Hills on the bight shows 
THE DOLERITE-SHEET BESTING UPON THE EVEN SUBFACE OF THE GbaNITE. 
Gregory, 1 The Great Rift Valley,’ 1896, p. 220. 
