186 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



northern line of drainage slopes gradually towards the canon north of 

 Ohonua village (Pis. 114, fig. 1; 212, fig. 4), and through this the water 

 collected in the valley comes out as a small stream. No outcrops of corallif- 

 erous limestone were found in the depression between the two ridges, except 

 on the western face of the eastern line of hills, where, at a height of about 

 525 feet, a small ledge was found surrounded by earth of volcanic origin. 

 Dr. Mayer ascended to a point a little over 600 feet on the west side of 

 the eastern hill range. As a rule, the soil of the western ridge is of 

 volcanic origin, of a light red brown or yellow color; the highest point 

 of the western ridge was about two and one-half miles from the village 

 of Ohonua. The soil of the bottom of the valley is also of volcanic origin ; 

 it is deep, of a dark red brown, and quite fertile. It was covei'ed with 

 large groves of cocoanut trees, pisonias, and a couple of species of Gar- 

 denia, in addition to numerous ferns and grasses ; no outcrops were found 

 in the lower parts of the valley. The fourth tei-race of the western 

 line of hills was probably 300 feet above high-water mark. We took sotne 

 photographs from the highest point of the western ridge to show the great 

 extent of the sink of the island (PI. 114), and also from other points along 

 the crest ; they plainly show that this is merely a valley of erosion, and that 

 the river at English Roads landing has cut its way through the western ridge, 

 and drains the valley as any other drainage valley would do. Other small 

 creeks run east from the slopes through the limestone country of the 

 western range, and disappear in the bottom of the valley at the foot of 

 the eastern range. At a distance of five miles from Ohonua village, the 

 bottom of the valley must be at least 120 feet lower than the highest point 

 of the western crest; it drops gradually to the level of the sea, following 

 the level of the creek which drains the interior valley and comes out at 

 English Roads. A number of fossils were found at a height of 300 feet 

 in the fourth terrace. 



Speaking of Eua, Lister * says : " The volcanic formation comes to the 

 surface over a great part of this high ground (the western slope of the highest 

 part of the eastern ridge), and when bare of vegetation it is readily recog- 



' Notes on the Geology of tlie Tonga Islands, by J. J. Lister, in Q. J. Geol. Soc, London, Vol. 

 47, 1891, p. 590. 



