418 E. O. HOVEY WALLIBU AND RABAKA GORGES 



of ash, and the surface vegetation was mostly destroyed, though the 

 vegetable mold and soil were not much disturbed, being simply buried. 



Wallibu Gorge and Valley 



the 



The immediate gorge of the Wallibu is bordered by bluffs ranging 

 from 50 to 150 meters in height. Where the stream issued from the 

 Muffs of solid old-land at the sea beside the Eichmond estate the gorge 

 is about 215 meters wide, as determined by pacing, and it gradually 

 diminishes to less than 5 meters about 3 kilometers from the sea, where 

 the permanent stream flows through a defile, the right bank of which 

 was formed by agglomerate, the left by the edge of an old lava bed. The 

 water filled the whole width of this defile, and was so deep and turbulent 

 when I visited the spot (March, 1903) that I progressed no farther in 

 my explorations of the bottom of the gorge. Above this point, however, 

 the gorge widens out again. 



It is impossible, perhaps, to estimate closely the amount of material 

 deposited in the areas drained by the two rivers in question, but it is 

 probably well within the bounds of fact to say that the average depth of 

 the debris left in the Wallibu gorge was not less than 30 meters, while 

 that in the gorge of the Eabaka was at least as great. 2 The depth of new 

 material thrown into the side ravines was likewise to be measured by 

 meters. The mantle of compacted dust (mud) along the southern rim 

 of the crater and on the upper slopes of the mountain draining into the 

 Wallibu was from half a meter to 2 meters in thickness in June, 1908, 

 after the loss of material due to the erosion of six rainy seasons. There 

 is every reason to suppose that as much or more ash covers the head slopes 

 of the Eabaka, but no sections of the deposit were observed here in June, 

 1908. In June, 1902, however, Mr G. C. Curtis and I came near losing 

 our way in gullies 2 to 4 meters deep in the new ash at the head of one 

 of the tributaries of the Eabaka, and more ash was cast on the slopes in 

 subsequent outbursts. 



To one who has been over the ground an estimate of 5 meters will not 

 seem excessive for the average depth of the ash over the "area of annihi- 



2 The estimate of 200 feet for the depth of the filling of the Rabaka gorge, as given by 

 myself (Bull. American Museum of Natural History, vol. xvi, p. 343) and Doctors Ander- 

 son and Flett (Philosophical Transactions of the Royal Society of London), were derived 

 from the same source, a Mr A. H. Spence, of Saint Vincent, and seems to have been ex- 

 cessive. The vertical sections quoted in a later part of the present paper show the 

 depth of the new filling to have been from 30 to 35 meters deep where the Rabaka 

 issues from the hills. Farther up stream the deposit was somewhat deeper, but 40 to 45 

 meters seems to be the maximum that can be assigned to the original depth of the new 

 debris thrown into the gorge by the 1902-1903 eruptions. 



