254 



DISTRIBUTION OF PLANTS. 



wards; dividing, subdividing, and diminishing in altitude until they 

 reach the sea. 



As the Vincennes approached and entered the harbor at Matavai, 

 the summit of Oroena continued in sight ; but was now less prominent, 

 with diminished grandeur in the scenery, the mountain ridges being 

 chiefly concealed by gently-rising, swelling slopes. 



Geological structure. Like most high ocean islands, Taheiti is 

 volcanic. It is however surrounded by a reef of coral; leaving open- 

 ings deep enough to admit large vessels, opposite the mouth of the 

 principal streams ; the inside passage, an eighth of a mile to a ndle 

 wide, affording sheltered boat-navigation around almost the entire 

 circumference. 



The mineral shore of the island is almost everywhere alluvial, com- 

 posed of blackish volcanic sand ; but here and there, a ridge extends 

 outwards to the sea in a rocky bluff. The prevailing rock throughout 

 the island, was observed to be compact, and was termed by Mr. Dana 

 " basaltic :" conglomerate or pebble-rock being occasionally intermixed, 

 and in some spots vesicular lava ; but there were no lava-streams, nor 

 active volcanoes, no pumice, obsidian, nor even hot-springs. In draw- 

 ing comparisons with the distant continents at the time of writing 

 my journal, I could not recollect meeting with either quartz, mica, 

 or mineral carbonate of lime on Taheiti. 



The marginal portion of Taheiti. In the vicinity of the sea- 

 coast, the climate is warm. On the North side of the island. Dr. 

 Fox found the subterranean or approximate mean annual temperature 

 "79° Fahr. ;" which is "higher than that of Brazil." The South or 

 windward side of the island, being less sunny with more rain, is pro- 

 bably cooler. Thunder was once heard, during our stay. From the 

 South side of Taheiti, the sunset of the 17th proved the most gorgeous 

 I ever witnessed; the clouds in the West being lighted up with sun- 

 like lustre ; with, in the East, a brilliant rainbow of several concen- 

 tric arcs, perfect for more than a semicircle. Residents spoke of 

 occasional "storms from the Westward;" rendering, during their 

 continuance, the harbor at Matavai "unsafe." 



On the North side of the island, the swelling slopes and ridges, 

 to the elevation of about a thousand feet, are barren and devoid of 

 trees ; and overgrown with tangled fern, a Oleichenia, here a foot or 

 two high ; grasses being so rarely intermingled as to occur singly. 

 Metrosideros viUosa, a low shrub having scarlet flowers, made its ap- 



