BY H. I. JENSEN. 645 



Most of what is seen on the surface is tachylitic or hemicrystalline. 

 A specimen of coarse-grained dolerite from the western end of 

 the island was shown to me, and is the only macrocrystalline 

 rock 1 have seen there. Holocrystalline fine-grained basalts 

 may be obtained in deep creek beds and sea cliffs where denuda- 

 tion has had time to work into the core of the flows. 



Drainage is naturally in a very youthful stage. The larger 

 streams, which run with great rapidity after rains and are at 

 other times a mere string of waterholes, are cutting deep trenches 

 and gorges. 



The surface of all the flows, old and young, is tachylitic and 

 highly vesicular, proving their recent nature. Besides the lava- 

 flow of 1902 and that of 1905-06, there are many flows of very 

 recent appearance which support but scanty vegetation, and have 

 soil only in the cracks and holes on the surface. As the lava 

 decomposes very rapidly under the influence of a moist climate, 

 especially as the surface is so porous, it is probable that these 

 flows are less than 500 years old. Such are the "Big Mu "* 

 between Aopo and Asau, the " Small Mu " between Aopo and 

 Sasina, the Papalaulelei flow (on the north side), and several other 

 flows on the south side of Savaii. 



The large and small flows of Aopo and one on the south side of 

 Savaii opposite the big "Mu" probably come from the Mauga 

 Afif crater or one of its parasitic craters in the west end of the 

 island. The Papalaulelei flow probably came from Mauga Pule 

 in the eastern end of the island. On all these flows the original 

 crust still exists, showing wrinkled, twisted, ropy, billowy, 

 hummocky and knobbed structures. Deep cracks formed by 

 cooling, partly in tilled with soil, and deep holes where trees have 

 been burnt out, holes formed by the falling in of the roof of lava 

 tunnels and smaller depressions (formed by the collapse of the 

 thin glassy lava crust, over caverns formed by the withdrawal of 

 he lava in the molten state after the crust hact formed) exist in 



" O le Mu" means "the burnt." 

 t " Afi," fire. 



