390 PACIFIC ISLANDS. 
But if the waters have been thus efficient in causing denudation 
and opening valleys, may not fissures or dikes have determined their 
courses! ‘The only test of truth, an appeal to facts, may answer the 
question. Mount Loa is a mountain yet unchanged. It has its dikes 
in great numbers : but over these dikes the country is more apt to be 
raised a little from the overflow of lavas than depressed, and this 
would turn off the water. Again, we see no instances of dikes yield- 
ing, and offering a course for a stream. As to unfilled fissures, there 
are few of them, and these, with rare exceptions, are immediately 
about the active vents. Is either supposition sustained by the facts 
presented? We know the tendency of water to take the lowest parts 
of a surface, and will it not follow these parts, whether or not there be 
a dike or fissure? It is obvious that whatever ravines or depressions 
the floods of lava may have left, would be the courses of the waters ; 
and these depressions would be followed to the sea, and ultimately 
become valleys. We may hence conclude that the waters would not 
wait till there was a convenient fissure; they would go where znclina- 
tton led, and make valleys with little difficulty, if there were no 
guiding or aiding fissures. Were the dikes filled by a rock more 
decomposable than those enclosing it, or more easily worn away, as 
is the case in some granitic regions, we should expect that they 
would frequently become water courses: but this is seldom the case 
in the Pacific islands. 
The valleys in some of the Canary Islands, extend from the shores 
drier seasons, (which, however, are of short duration on this, the windward coast,) fords 
the shallow streams without difficulty, gives the following account of his journey during a 
time of rains. ‘Great and continued rains fell during my absence, and the numerous 
rivers became so swollen and furious that the very sight of them was fearful. These 
raging streams crossed my path about once in half a mile for a distance of about thirty 
miles, and I was compelled to pass them to return home. Most of them run at a rate 
of twenty or thirty miles an hour, and in their course there are numerous cataracts from 
ten to a hundred and fifty feet in perpendicular descent. ‘Though the torrents were so 
fearful as to make one almost quail at the thought of struggling with their fury, ropes 
were provided, and several men employed for the adventurous task. Great calmness and 
presence of mind, and great energy and muscular effort, were required to retain one’s 
grasp of the rope, and buffet with the foaming flood. We at last succeeded, though at 
imminent peril. At one of the rivers, we spent three hours in finding a place where we 
might, with any degree of safety, extend our hawser across, and transfer our party to the 
opposite bank. The streams are at the bottom of narrow ravines, with the banks exceed- 
ingly precipitous, and often perpendicular bluffs of basaltic rock.”—Miss. Herald, 
Xxxvill. 157. 
