17.

By the blue rushing of the arrowy Rhone.

Stanza lxxi. line 3.

The colour of the Rhone at Geneva is blue, to a depth of tint which I have never seen equalled in water, salt or fresh, except in the Mediterranean and Archipelago.

[The blueness of the Rhone, which has been attributed to various causes, is due to the comparative purity of the water. The yellow and muddy stream, during its passage through the lake, is enabled to purge itself to a very great extent of the solid matter held in suspension—the glacial and other detritus—-and so, on leaving its vast natural filtering-bed, it flows out clear and blue: it has regained the proper colour of pure water.]