1889 - 90 .] Mr C. Michie Smith on Volcanic Eruption. 69 
only for a few minutes at long intervals, made it impossible to get 
really good views. The great Y-shaped cutting is, however, clearly 
seen, and it should be noted that, judging from photographs taken 
soon after the eruption, and from the descriptions given by visitors, 
this cutting is entirely due to erosion. 
The minor details of the water action were no less interesting. 
The loose debris was, as has been mentioned, mixed with large 
blocks of stone. One of these, distant some 2J miles from the 
crater, measured about 18 feet by 13 feet by 13 feet, and still larger 
blocks were met with higher up. Now when the water had cut 
down to such a block it behaved in one of several ways. In some 
places, where the eroded channel was wider than the block, passages 
for the water were cut round one or both ends, and the block itself 
gradually sank down as the material on which it was supported 
was cut away. In some cases, where the block was long enough 
to bridge the channel, a tunnel had been made under it through 
which all the water passed. In other cases waterfalls of considerable 
height had been formed by such blocks. In these cases the large 
block was protected on its upper side by a number of smaller stones, 
which prevented erosion from taking place behind it. The conse- 
quence of this was that the bed of the stream for some distance 
back became nearly horizontal, and the carrying power of the water 
was greatly decreased, thus tending to make the falls permanent. 
It is not to be supposed that they will be really permanent, as the 
blocks will gradually be undermined by the water falling over them, 
but their existence at present illustrates the way in which differences 
in slope in the bed of a torrent may have been brought about by 
obstacles which have long since been removed. As seen from above, 
there were three main lines of erosion, but that along the old 
bed of the Biwasawa was by far the most prominent. In addi- 
tion to these principal channels there were numberless tributary 
channels, reproducing in miniature all the details of mountain 
sculpture. 
In a few years the materials forming the earth-stream will 
consolidate into what will probably be classed as a volcanic breccia, 
and erosion will go on much less rapidly. The consolidation has 
indeed already begun, and it was interesting to notice how a sort of 
laterite was forming out of the more ferruginous materials, which 
