BY D, MAWSON. 475 



been considerable and permanent during that period. It is pro- 

 bable though that, in the early Tertiaries, with the development of 

 further folding, the land began to break up,"**" until, as now, so little 

 of the original remains. Evidence available in New Caledonia and 

 New Zealand dates the commencement of this folding to a period 

 subsequent to the Cretaceous, whilst unconformities in the later 

 rocks of the New Hebrides are proof of its continuance down to 

 the present time. Extreme upheaval, which in Santo and 

 Malekula has laid bare a continuous series, from horizontally 

 bedded recent raised reef debris above, to a basis of folded 

 Miocene below, allows of a critical enquiry into the nature of 

 the movements which have contributed to the present topography. 

 Analysing this evidence, it would seem that earlier features in 

 the development were of the nature of true folding, but that 

 later tendencies had been towards almost horizontal uplifts, 

 resulting in a maximum elevation above sea-level of perhaps 

 4000 feet, t 



Extended observation in South Pacific tectonics seems to 

 show that a similar cycle of operations has been most widely 

 exercised. The interesting result is therefore arrived at that 

 more or less horizontal positive and negative movements are often 

 a feature of the later phases in mountain-building. 



Situated as this region is in a tropical climate, these slow, 

 progressive, and fairly regular movements have been faithfully 

 and indelibly recorded by the industrious coral polyp, whose 

 mode of life has resulted in the development of three main types 

 of islands, from as many possible land-movements. 



* Just as the East Indian Continent is known to have " gradually and 

 irregularly broken up," Wallace, A. R., " On the Physical Geography of the 

 Malay Archipelago." Journ. Geogr. 8oc. xxxiii. 233, 1863. 



t See Parti. Seel. Santo. The fact that some mountain-ridges owe 

 their elevated position to nearly horizontal uplifts through considerable 

 heights has been clearly demonstrated by Prof. W. M. Davis, ' ' The bearing 

 of Physiography upon Suess' Theories," xix. 265, 1905. Also by the same 

 author, "The Geographical Cycle in an arid Climate," Journ. Geol. 1905, 

 p. 381. 



