composed mainly of Sphærella nivalis. This red scum appears to thrive especially where such pools have been enriched in nitrogenous matter by water which has run down the rocks and taluses where great numbers of birds resort for nesting. It is often found that a glacier or snow-patch is coloured red when water flows over it from rocks where birds are nesting, and the well-known Scottish Arctic explorer Lamont, who has so ably depicted many an Arctic scene and incident, has ascribed the colour as being due to the droppings of the rotge, or little auk, which are, as he points out, of blood-red colour. But I have examined such patches of red snow and ice microscopically, and have found the redness due to the presence of the red snow alga. It is certain, however, that the droppings of the rotge will so enrich the water with nitrates that the red alga, which is growing plentifully, though invisibly, on the black rocks and ground, thrives exceedingly and is carried, and lives and grows on the melting surface of the snow or glacier ice. I have seen glaciers coloured green and black as well as red. The green colour is certainly due to green algæ, and the black, in certain cases, I have found to be due to fragments of desiccated lichen, fragments which do not appear to be growing on the ice but are there just as any other dust might be.
