II EVIDENCE OF RECENT EMERGENCE 15 



low-lying plains that constitute the sea-border between Lekutu and 

 Ravi-ravi Point. As shown in the profile-section on p. 62, these 

 low coast districts are prolonged inland, with an average rise of 

 between 20 and 30 feet in a mile, to the heart of the island ; and 

 we have here an extension inland of the slope of the submarine 

 platform. These broad inland plains, and I may here include 

 those behind Lambasa, are covered over much of their surface with 

 submarine tuffs and clays in such a manner that we may almost 

 trace their continuity at the coast with similar deposits now in 

 actual formation beyond the low-water level on the surface of the 

 submarine platform. 



A glance at the map of the island, where these inland plains 

 are indicated by the 300 feet of the contour-line, will make this 

 point more clear. These plains are traversed by the Sarawanga, 

 Ndreketi, Wailevu, and Lambasa rivers ; and so slight is the fall 

 that cutters usually ascend the rivers for several miles, whilst the 

 tide extends for a considerable distance up their courses. That 

 the emergence of the inland plains of Kalikoso in the eastern part 

 of the island is comparatively recent there can be but little doubt. 

 In that locality as described on page 224, the low marshy land, 

 surrounding the fresh-water lake of Vakalalatha, although five 

 miles inland, is only elevated 20 to 30 feet or less above the sea, 

 and silicified corals are scattered over its surface. 



There is one other method of ascertaining the character and 

 amount of elevation that may be still in progress in this island 

 namely the comparison of the results of surveys of the coasts at 

 different periods. In this manner data may be obtained as regards 

 the growth of the mangrove belt, changes in size of the low reef- 

 islets and islands, and alterations in depth. For this purpose I 

 have employed the charts of the north and west coasts of the 

 island made by Commodore Wilkes in 1840^ and the Admiralty 

 charts 379 and 382 as completed from the survey of these coasts 

 by Commander Combe in 1895-96. 



It was not easy to make many good comparisons in the case of 

 the advance of the mangrove-belt of the main coast. There 

 certainly has been no great advance seaward of the margin of the 

 mangroves in this half century. The average amount probably 

 lies between the estimate obtained for the coast opposite Mathuata 

 Island, where there has either been no change or an advance of 

 only icxD yards or so, and that for the advance seaward of the 



^ A^ias 0^ the United States Exploring Expedition, vol. i., Philadelphia, 

 1850, 



