ORIGIN Or THE U-SHAPED VALLEYS 415 



the deforestation of the mountains and the deposit of a mantle of loose 

 ash on the denuded slopes might be greatly multiplied from both Mar- 

 tinique and Saint Vincent, but those given suffice to make clear the points 

 that the valleys under consideration have been traversed frequently by 

 streams of thick pasty or semi-fluid matter, and that these streams were 

 armed with angular and subangular sand and gravel, by means of which 

 they excavated U-shaped gorges in the beds and dikes of rock encountered 

 in their course. 



It is improbable that this corrasion of a U-shaped section should con- 

 tinue after the watershed becomes covered again with vegetation, because 

 then there will be no accumulating supply of loose angular material to 

 form mud flows and provide the floods with grinding tools. Nor is it at 

 all likely that the phenomenon described is a new one or has been pro- 

 duced even in Saint Vincent by the recent eruption alone. The rock 

 beds in which these U-shaped gorges are so beautifully developed lie in 

 the lower reaches of the Larikai, Eoseau and other valleys through which 

 has been carried debris of the numerous eruptions of the Soufriere that 

 have constructed the entire upper 1,000 meters of the volcano. 



Where the crevicing of the rock-mass has been favorable, the impact of 

 stones hurtling down the stream bed has broken off chips from the bed 

 rock, producing a good imitation of the "chatter" marks made by a 

 glacier. 



The cross-section of the gorges of the headwaters of the Wallibu, the 

 principal stream of the leeward side of the mountain, was not observed 

 except from above, on account of the inaccessibility of the region. The 

 lower and accessible part of the Wallibu gorge is through beds of old 

 agglomerate, with here and there a comparatively small bed of old lava. 

 The very bottom of the gorge is usually concealed by the fresh debris 

 brought down since the recent eruptions, but where the sides are of the 

 agglomerate they come abruptly and sometimes almost at right angles to 

 the floor. The stream is aggrading this part of its bed. About 3 kilo- 

 meters from the coast one encounters rock forming the bottom of one 

 side of the gorge and suggesting a U-shaped section, except where the 

 columnar structure of the lava beds has caused the section to be nearly 

 or quite rectangular. 



All the streams of the denuded portion of the Soufriere on its wind- 

 ward side are tributaries of the Eabaka river. The principal are four in 

 number, and they have deeply incised the side of the cone, exposing to 

 view several massive beds of lava forming the floor of the valleys at dif- 

 ferent levels. Each bed ends down stream in a precipice, hence there are 



