282 CORALS AND CORAL ISLANDS. 
tion Report; but that this is the means of attaining great 
width and thickness with no aid from subsidence is the new 
view of Mr. Murray. The method has been described in the 
words: Reefs grow out on their own talus. The view is 
supported by Dr. Guppy, Mr. A. Agassiz, and others. 
a. Mr. Murray’s observations were made at Tahiti. He 
reports the following facts derived from soundings off north- 
ern Tahiti, made under his supervision and that of the sur- 
_veying officer. 
Along a line outward from the edge of the barrier reef 
there were found: (1) for about 250 yards, a shallow region 
covered partly with growing corals, which deepened seaward 
to 40 fathoms; (2) for 100 yards, between the depths of 40 
and 100 fathoms, a steeply but irregularly sloping surface 
which commenced with a precipice of 75° and had a mean 
angle exceeding 45°; then (3) for 150 yards a sloping bot- 
tom 50° in angle; (4) then a continuation of this sloping 
surface, diminishing in a mile to 6°, at which distance out 
the depth found was 590 fathoms (3,540 feet). Over the 
area (2), or the 100 yards between 40 and 100 fathoms, the 
bottom was proved to be made of large coral masses, some of 
them “20 to 30 feet in length,” along with finer debris; out- 
side of this, of sand to where the slope was reduced to 6°; 
and then of mud, composed ‘of volcanic and coral sand, 
pteropods, pelagic and other foraminifers, coccoliths, etc.” 
These observations have great significance. They show 
(1) that the feeble currents off this part of Tahiti carry little 
of the coral debris in that direction beyond a mile outside of 
the growing reef; (2) that a region of large masses of coral 
1 Dr. Archibald Geikie gives in his Presidential Address before the Royal 
Physical Society of Edinburgh in 1883 (Proc. viii. 1, 1883) a section of the soundings 
“on a true scale, vertical and horizontal,” and in it the upper steepest part of this 
100 yards has a slope of about 75°. 


