REVIEWS 481 
is open to another interpretation. It may be explained as the outer 
margin of a continental shelf that has been gradually forming through 
late Tertiary and Quaternary time, the final touches having been given 
to it in post-Glacial time by the action of waves and currents on the 
fine silts that are so abundantly supplied by the inflowing rivers; the 
sea water is today sometimes discolored 60 km. from the river mouths. 
It may be recalled in this connection that Daly has found that “the 
charts of the world show the break of slope on the [continental] shelves 
to be near the 4o-fathom line,” and that it is only to this depth that 
“waves and currents are competent to advance the outer edge of a 
continental embankment with noteworthy speed.’ Hence, instead of 
interpreting the 40-fathom edge of the Sunda Sea bottom and the edges 
of many other continental shelves of like depth as marking continental 
shore lines when the ocean was lowered in the Glacial epochs—the ocean 
lowering being calculated, singularly enough, to have been but little 
less than the same measure of 40 fathoms—these shelf edges are better 
interpreted as being due in significant measure to the adjustment of the 
submarine profile to normal sea-level by submarine processes in post- 
Glacial time. 
Coral reefs are rare or wanting in the Sunda Sea by reason of the 
muddiness of its bottom and the resulting impurity of its waters, as 
Sluiter explained thirty years ago. But the margin of the eastern part 
of the sea floor, the so-called Borneo bank, is occupied by an imperfect 
and discontinuous barrier reef for over 450 km. Molengraaff points out 
that the reef is separated at its easternmost extension only by the 
50- or 60-km. width of the deep-water Macassar Strait from the island 
of Celebes, while it is separated by 160 km. of shallow water from Borneo; 
hence it is related not to the nearer but to the farther one of these islands. 
The imperfection of the reef is ascribed to the muddiness of the sea- 
floor margin on which it is assumed to have originated as the ocean rose 
in post-Glacial time; but the muddiness of the shallow sea floor is so 
great that it is doubtful whether any reef could have originated there 
at all. ‘The reef may perhaps be better explained as a recent upgrowth 
from such parts of a Tertiary reef as were not overwhelmed and destroyed 
by detrital deposits in the extension of the shallow sea floor while the 
ocean was lowered in Quaternary time. 
Mention may be made of a number of imperfect atoll reefs which 
Molengraaff describes as bordering several extensive 20-40-fathom 
shoals that rise from deep water east of the Sunda Sea, in the region 
between the stable western islands and the unstable eastern ones. The 
