GEOLOGICAL OHSKHVATIONS I\ FLH. 79 



and the erosion of the volcano to maturity re(iuire much time. It has 

 been interred that the planation of the elevated limestones of the 

 Exploring group by wave-cutting may have occurred in the Glacial 

 epoch. If Munia existed at that time, its slopes should have been 

 cut by deep valleys and the valley-mouths should have been drowned 

 at the close of the epoch. Since, however, the embayment of the 

 coast of Munia is very slight, it is believed that the island was formed 

 in late Glacial or early post-Glacial time; yet at a time sufficiently 

 remote to permit of the mature erosion of the volcano. The elevated 

 limestones underlying the debris from Munia are Pleistocene or Recent 

 in date and hence confirm the evidence just given. 



Kanathca. 



The main portion of Kanathea is built on the remnants of an older, 

 eroded volcano. Such remnants are still visible. No limestones 

 appear; if they ever formed part of the island mass above sea, they 

 have been lost by erosion. 



The more recent part of Kanathea is built up of agglomerates and 

 fiows which have been carved into a sub-mature topography. The 

 northwestern slopes of the island are little dissected and the slopes 

 generally follow the initial dips of the volcanic beds. The eastern 

 or windward side of the island has, however, deep, mature valleys. 



The southern third of Kanathea is genetically distinct from its 

 northern portion, and apparently represents a relic of the older ^'ol- 

 cano. Whereas the northern area is lateritized to a depth of but 2 

 or 3 feet, the southern has a late-mature topography of rounded hills, 

 lateritized to depths of 15 to 20 feet. 



Through northern Kanathea a central depression crosses the island 

 from northeast to southwest. Entering this depression from the 

 northeast, precipitous^ cliffs of agglomerate, 200 to 300 feet in height, 

 are seen on either side. The dips of these beds are quaquaversal 

 from a point somewhat east of the center of the valley. The lack of 

 any streams competent to erode such cliffs and the quaqua^'ersal 

 structure of the agglomerates indicate that the central depression 

 represents a crater. This crater has been breached. 



A glance at the chart of Kanathea will show that the island has a 

 long, narrow barrier reef extending to the northeast towards the 

 Exploring group. The lagoon within the barrier reef is free of islands 

 and has an average depth of 10 to 15 fathoms. The barrier reef 

 ranges along the eastern and southern sides of tlie island; elsewhere 

 the reef is fringing. 



