Reconnaissance by Submarine — Brock and Chamberlain 
383 
from the escarpment between the Penguin 
Banks and Mamala shelves. These samples were 
all well indurated reef limestone. No basaltic 
cobbles nor pebble-size fragments nor basaltic 
outcrops were seen on the Penguin Banks or 
Mamala shelves. 
The rounded boulders observed at the base 
of the escarpment between the Lualualei and 
Mamala shelves and the escarpment itself ap- 
peared to be basalt, though no samples were 
taken of either. Fragments of basalt were 
numerous in the channels cutting through this 
