BY H. B. GUPPY, M.B., SURGEON, R.N. 957 



greater depth than 60 fathoms, and seldom more than 40 fathoms" 

 but he met it with the explanation that such lagoons are being 

 filled up, pari ])ctssu with the downward movement, by the growth 

 of corals and the accumulation of sediment (Coral Reefs, edit., 

 1842, p. 115.) In the second of two papers by Prof. Arch. Geikie, 

 published in "Nature' 1 " (Dec. 6th, 1883) on "The Origin of 

 Coral Reefs," -where the arguments for and against the theory of 

 subsidence are fully examined, the more recent views advanced by 

 Mr. Murray and Prof. A. Agassiz are dwelt upon at some length. 

 My observations on the raised calcareous formations in this Group 

 go far to support the modification in Mr. Darwin's theory which 

 appears to have become necessary ; but since these observations 

 aud my collections are now in the hands of Mr. Murray, I must 

 at present forbear from further remarks on the subject. It may 

 not however, be out of place to observe that amongst the reefs I 

 have examined in this group I have not found evidence of the 

 solution of the coral-rock taking such an important part in the 

 formation of lagoons as is implied in Mr. Murray's description of 

 the reef at Tahiti. 



The leading points of my paper I may briefly summarise as 

 follows : — 



(1). That reefs of the barrier class exist in Bougainville 

 Straits, a region which has been undergoing upheaval 

 during a prolonged period. 



(2). That these reefs may be arranged in two classes, (a) 

 those which have been formed at the present sea level ; 

 and (b) those, which having experienced upheaval, are 

 now represented by lines of islands and islets of coral 

 limestone, varying in elevation between a few feet to 

 over a hundred feet above the sea, their lagoon channels 

 being still preserved but often very shallow. 



(3). That the Shortland Islands have been produced by the 

 successive advancements of lines of barrier-reefs from a 

 nucleus of land of volcanic formation during a period of 

 upheaval, a process which resembles that by which, 



