94 ROYAL SOCIETY OF CANADA 



sheet ice, and that again covered by a very thin, but white, opake 

 deposition of hoar frost. From under this ice the water, flowlng 

 rapidly over the gravel bed below, had no ground-gru for a space of 

 eight or ten yards downwards. 



Above this rapid, a pool of moderate stillness, about three or four 

 feet deep, extends a hundred and fifty yards in length. Over the 

 bottom of this there were scattered, in an irregular manner, many 

 cauliflower-shaped clusters of silvery gru, most of them very small, and 

 none that were observed covering more of the bottom than a square 

 foot or two at one place. In the deepest and stillest part of the pool 

 there were several tufts of water starwort, with sooty-coloured decaying 

 leaves, forming the darkest-coloured objects seen at the bottom. These 

 were all densely tangled with fringes of silvery gru. At the head of 

 the pool, where the velocity acquired by the water in the rapid imme- 

 diately above it was not yet greatly diminished, an appearance of a 

 diflerent kind presented itself. There are here several largg stones 

 in the bed of the stream, but none of them projecting above the water. 

 On the faces of those opposed to the stream there were seen quantities 

 of gru of a different aspect from that further down. It was not 

 arranged in the same cauliflower shapes, but in angular masses, like 

 wreaths of snow blown by the wind. It wanted, too, the silvery glance 

 of the other, and had more the appearance of a pale ash-coloured mud. 

 ■On reaching it with the end of a pole, its consistency was found to 

 be less firm; in fact, it was only a heap of detached uncemented spiculse 

 pressed against the stones, and retained there mechanically by the action 

 of the water, in a certain modified state of its velocity. The source 

 of these heaps of uncemented spiculEe will soon be noticed. This 

 pool, as indeed was the case with all the pools in the river, had at 

 its edges and in its little bays narrow pieces of surface-ice, extending 

 a foot or two from the banks. 



The rapid immediately ahove this, not unlike that at the bridge, 

 was covered at the bottom with silvery gru, with one exception. The 

 river was low at the time from long-continued deficiency of rain, and 

 the water had deserted the south side of the channel, leaving many little 

 pools among the stones, communicating more or less freely by irregular 

 little currents with the main stream. The pools were covered over 

 with sheet-ice, and that with a thin opake deposit of hoar frost-like 

 snow. In the little currents returning from under this ice there was 

 no frozen matter. 



At the head of this rapid there is a pool much deeper and stiller 

 than that above the bridge-rapid already described. The depth is five 

 feet, and the stillness such that, at many points of it, there is no 



