[BARNES] ANCHOR-ICE FORMATION 95 



ripple or wave on the surface. None of the silvery cauliflower-like 

 ice was seen on the bottom here; but near the head of it, in a modified 

 state of the current pouring in from the rapid above it, there were, 

 on the faces of several large stones opposed to the stream, collections 

 of uncemented icy spiculas. 



The source of these collections was very readily observed in a great 

 rapid immediately above this. In that rapid the water has a much 

 quicker descent than in the others referred to. It is about a hundred 

 yards long, and cumbered with many large stones, pver which, -at 

 many points, through its whole length, the water breaks with a great 

 deal of spray. Here an immense quantity of gru occupied the bottom, 

 impeding much the course of the stream. At the time of observation 

 many pieces of this gru were seen edging up, and in some instances 

 breaking quite away from the bottom, apparently by the increasing 

 pressure of the water, as it became dammed back by the increase of the 

 gru itself. This at least was the appearance, although there may 

 have been another cause for the disengagement of it from the bottom, 

 and that is, the impeding, by the imperfectly translucent gru, of that 

 radiation of heat from the bottom which, I trust in conclusion to 

 demonstrate, is the immediate chief agent in the whole phenomenon. 



It is now to be observed, that a number of pieces of loose grn, 

 the origin of which was so clearly ascertained at this last rapid, were 

 floating down in all parts of the river. In passing through the rapids, 

 they were broken into fragments, and, where the fall was violent, 

 shivered into minute pieces. The larger pieces that remained after 

 passing through the rapids floated at the surface, immediately as they 

 got into the uniformly flowing currents at the heads of the pools; but 

 the minuter ones, mixed with the water to all depths by the plunging 

 whirls in the rapids, not being so speedily disentangled from their 

 cohesion with the water, by the action of gravity, floated for a greater 

 distance im^aersed in the water, and were intercepted by, and mechanic- 

 ally retained against, the faces of the stones by the action of the 

 stream at the heads of the pools. Further down, and in stiller water, 

 where no such intercepted heaps were seen, their buoyancy had, no doubt, 

 by degrees, overcome the cohesion and raised them to the surface; and 

 in fact, in the still water, many minute icy fragments were floating 

 in the surface. 



Mr. Knight, the celebrated botanist, quoted by M. Arago, has 

 obviously, in part, but not completely, distinguished between the 

 " frozen matter which reflected a silvery kind of whiteness," which 

 covered the stones in the rocky bed of the river, and " floating spiculse 

 under water," which he found to " accumulate much more abundantly 



