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GEOLOGY: W. M. DAVIS 
sive changes thus inferred. Sector G shows part of a group of confluent 
volcanoes, the area of which is about the same as that of the present 
Exploring Isles lagoon; several smaller cones rise near by; all together 
they resembled the present Lipari islands of the Mediterranean. After 
suffering prolonged dissection and partial submergence, the resulting 
embayed islands encircled by an upgrowing barrier reef are represented 
in sector H; this stage corresponds to that of Kandavu and its neigh- 
bors in southwestern Fiji. Down-sinking of the volcanic islands and 
upgrowth of the barrier reef continued until the total subsidence meas- 
ured X + 600 + y feet, when but few volcanic hills survived, as in 
sector J; the small Gambler islands in a large lagoon southeast of the 
Paumotus, or the small islands of Budd reef in northeastern Fiji repre- 
sent this stage. An uplift of 600 + y + > 100 feet then occurred, as 
in sector K: the resulting limestone plateau is typified by the uplifted 
atolls of the Loyalty group. The compound mass thus exposed to 
erosion was reduced over most of its limestone area to low relief sur- 
mounted here and there by residual hills, as in sector L; the hills of 
volcanic rock have smooth soil-covered slopes, those of limestone have 
steep cliffs and ragged crags. A recent submergence of 100 feet or 
more introduced the present conditions, as in sector M, where the 
lagoon floor has been smoothed by renewed deposition. 
The exterior volcanic islands, a, b, c, d, of sector G, must have suf- 
fered essentially the same series of changes as the larger central vol- 
canic islands. The atoll built on the largest cone, a, may have shown no 
volcanic knob in the stage of sector J, but one is afterwards laid bare 
in sector L, and its summit remains visible, along with a limestone 
knob, in the largest reef ring of sector M. Island b having a less initial 
height in sector G, it now shows only limestone knobs, sector M. 
Island c, beginning as a small volcanic cone, sector G, was deeply 
covered with limestone in sector J, and reduced to a low surface without 
high limestone knobs in sector L; and this is reasonable enough, for 
its area is not so large as any one of several uninterrupted lagoon areas 
within the adjacent great barrier reef. Its present reef is the result 
of upgrowth during the subsidence which transformed sector L into 
sector M. 
Seven of the twelve outlying reefs near the Exploring Isles are 
true atolls, Hke the true atoll of sector M. The foregoing discussion 
gives, I believe, a nearer approach to a demonstration of the origin of 
these sea-level atolls by upgrowth during sub-recent subsidence than 
has been provided for any other sea-level atolls, except Funafuti which 
has been penetrated by a deep boring. The smallest reef in sector M 
