TAHITI AND EIMEO. 49 



stream called Pappiamatia, about twenty yards wide, and from two to 

 three feet deep, running down it. About five miles from the coast 

 they passed a range of basaltic columns, one-fourth of a mile in 

 length; the cliff presenting a perpendicular wall, rising up at the 

 east side of the stream, formed columns, one hundred and fifty feet 

 high; the number of sides varied from four to seven, and their 

 diameter from nine inches to two feet. The ridge at whose base this 

 was found, was upwards of two thousand feet high. The party 

 reached Matavai Bay at sunset. 



The ridge that our gentlemen followed, is considered by them as 

 the most feasible route to the summit of Orohena; the greatest 

 difficulty with which the attempt is attended arises from the dislike 

 of the natives to visit places where they have not been before, and 

 their anxiety to keep themselves within the region of the fahies. 



Pitohiti might also be reached by the same route ; there is little 

 doubt that the latter has also been ascended by following the western 

 branch of the Pappino valley, a route which was also considered 

 feasible by our party ; a third route might also be found by following 

 the main branch of the Pappino, which, as will be seen on the map, 

 rises behind Pitohiti. 



This excursion furnished more full information, in relation to the 

 nreolooncal structure of the island than had before been obtained. 

 This is exclusively volcanic, and the rocks are either compact basalts, 

 or conglomerates of basalt and tufa, although no active volcano exists, 

 nor any well-defined crater, unless Lake Waiherea can be considered 

 as one. Through these rocks olivine and pyroxene are copiously 

 disseminated; cellular lava was found in some places, but neither 

 pummice nor obsidian ; quartz and mica were not observed, nor any 

 carbonate of lime, except in the form of coral rock. 



There is no conformity between the rocks of the centre of the 

 island and those which in most places extend inwards for a few 

 miles from the coast. The former are usually compact, of columnar 

 structure, and exhibit no appearance of horizontal stratification ; the 

 latter lie in horizontal layers, composed of scoriaceous and vesicular 

 lava. In both of these structures, singular twistings and contortions 

 were observed. Many dikes were seen to occur, not only in the 

 mountains, but near the sea-coast ; these were from three to six feet 

 in width. 



All the rocks of the island appear to be undergoing rapid decom- 

 position. Even in places where the rock seemed to have retained its 



VOL. II. 13 



