578 H. B. GUPPY ON THE RECENT 



that was once submerged. Then there are islands in which the volcanic peak 

 has become an eccentric nucleus, from which line after line of barrier-reef has 

 been [advanced overlying the volcanic muds, islands in which I did not find 

 the coral limestone of a thickness of 100 feet. Then we have the 

 upraised atoll, such as Santa Anna, which, within the small compass of a 

 height of 470 feet, displays the several stages of its growth, — first, the 

 originally submerged volcanic peak, then the investing soft deposit, and over 

 all the ring of coral limestone that cannot far exceed 150 feet in thickness ; 

 lastly, we come to the mountainous islands formed of old volcanic rocks, 

 such as St Christoval, which, although over 4000 feet in height, showed 

 to me no calcareous envelopes at a greater height than 500 feet above the 

 sea, the coral limestone crust being even thinner than in the smaller and more 

 recent islands. 



I purpose now to draw four limited inferences from these facts of observa- 

 tion, 'without reference to any particular view that may be held on the subject 

 of the formation of coral reefs, and to compare such inferences with the prevail- 

 ing views on that subject. 



(1) That these upraised reef-masses, whether atoll, barrier-reef, or fringing- 

 reef were formed in a region of elevation. — This is self-evident. The last upheaval 

 that occurred, of which I found proofs in different parts of the group, was to 

 the extent of about 5 feet, but at the present day there are signs of this move- 

 ment being still in operation; and for the purposes of future observation I have 

 established datum-marks in different islands. This, therefore, being a reign of 

 elevation, it is apparent that that portion of Mr Darwin's theory of coral reefs, 

 which ascribes the formation of atolls and barrier-reefs to a movement of sub- 

 sidence, cannot be applied to the islands of the Solomon Group, since we here 

 find upraised atolls and barrier-reefs associated with existing reefs of the same 

 description. This conclusion accords with the results obtained by Professor 

 Semper in the case of the Pelew Islands, and by Professor A. Agassiz in the 

 case of the Florida reefs. 



(2) That such upraised reefs are of moderate thickness, their virtual measure- 

 ment not exceeding the limit of the depth of the reef-coral zone. — Amongst 

 the numerous islands which I examined I never found one that exhibited 

 a greater thickness of coral limestone than 150 feet, or at the very outside 200 

 feet. One of the corollaries of the theory of subsidence is concerned with 

 the great thickness of atolls and barrier-reefs. My observations in this region, 

 and it is such regions that can alone afford such evidence, show that atolls and 

 barrier-reefs can be formed with no greater thickness than they would possess 

 in accordance with the depths in which reef-corals thrive, the vertical thickness 



of the reef not exceeding the depth of the reef-coral zone The only 



objection worthy of attention that has been advanced against the atoll-theory 



