1908] on Ice and its Natural History. 273 



about half an hour, a strange rattling sound was heard, which &very 

 moment grew louder, without it being possible to say what caused it. 

 At length it explained itself by the bed of the stream in front of the 

 anchorage of the ship in which I was, suddenly filling with brown 

 muddy water, descending with great velocity to the sea and charged 

 with vast quantities of stones, sand and mud. The rattling noise 

 was produced by these stones and rocks being driven violently over 

 the rocky bed and against each other by the current, against which 

 nothing could stand. Naturally all the other river beds in the island 

 fared alike. Their accumulations were washed away into the sea 

 likewise. The rocks of Tenerife are volcanic and produce in 

 weathering, besides kaolin, hydrated oxide of iron and other ochre- 

 ous substances, which have a reddish colour. The consequence was 

 that for nearly a week the island was surrounded by a fringe of red 

 water. The quantity of rain which fell was so great that when it 

 reached the sea it floated on the top and retained in suspension the 

 fine ochreous mud, which would have been precipitated by mixture 

 with the sea-water had the supply of fresh-water been less abundant. 

 A still more remarkable instance of this kind is related by the 

 Prince of Monaco. At the end of August 1901, he visited the island 

 of San Antonio in tlie Cape Verde Group. Here rain is very scarce. 

 It was said that it had not rained for three years. He landed 

 opposite the entrance of the valley of Tarrafal and took a photo- 

 graph, in which the dry river bed, encumbered with rocks and stones, 

 occupied the foreground. About noon a cloud-burst occurred from 

 which it was necessary to take shelter for a considerable time. On 

 returning to the landing-place to rejoin his ship, he found that the 

 stream had cut out a broad bed in the stones more than a metre in 

 depth and precipitated the whole of the debris into the sea. He 

 photographed the river-bed after this catastrophe, and the pair of 

 photographs constitutes one of the most important documents in 

 the natural history of denudation. By the kindness of his Highness 

 I am permitted to reproduce these photographs. Fig. 6« represents 

 the view in the morning. Dr. Portier, the well-known bacteriologist, 

 is standing on the gravel plain in front of the larger boulder, and 

 the whole of his body is visible over the smaller boulder in the 

 immediate foreground, which is nearly covered by the gravel. 

 Fig. 6& represents the same view in the evening, after the stream has 

 done its work of distributing the accumulation of debris due to three 

 years' chemical and gravitationcd degradation. All that is now seen of 

 Dr. Portier, over the top of the nearer boulder which has been almost 

 completely undermined by the torrent, is the top of his helmet. The 

 stones in the river-bed in the morning were as round as those oc- 

 curring in any perennial river, yet it was impossible in^ this case for 

 the river to have had anything to do with the rounding of them. 

 The sole function of the river in this island is, once every year or so, 

 to clear the bed of rounded stones, not to make them. 

 . Vol. XIX. (No. 102) t 



