24 Journal of Travel and Natural History 



I was not a little suri3rised in May 1852, whilst crossing the 

 salt waters of the Tagus, from Lisbon to Lavradio, to observe, in 

 approaching the opposite shore, that the ordinarily bluish-green 

 waters of that majestic river, had suddenly become of a violet 

 purple colour. A closer examination, however, of the colouring 

 substance soon taught me that this unusual hue had been caused 

 by the presence of a species of Protococcus, which is generated in 

 vast quantities in the extensive neighbouring Salinas. 



Several years previously, Messrs Turrel and Freycinet, whilst 

 sailing round Cabo d'Espichel, on the Portuguese coast, observed 

 the Atlantic ocean glittering with a blood-red colour to the extent 

 of many miles; and the subsequent investigation of this coloured 

 sea water by Montagne, proved that myriads and myriads of a red 

 Protococcus * had imparted this tint to the ocean. 



It would be an easy task to cite many more examples of this 

 great phenomenon in temperate regions; but I have said enough 

 to prepare the reader for its occurrence on the African continent, 

 in equally rich variety. I saw it immediately on first setting foot 

 on the west coast of Africa, in September 1853. I landed at 

 Freetown, Sierra Leone, and I there found the walls of the houses 

 facing the north jminted like maps, with black, bronze, green, 

 and violet spots, reaching from the basement up the gable. On 

 closer investigation, these proved to consist of a felt-like accumu- 

 lation of several small species of algae, which could be taken 

 off the walls almost like paper-hangings. Even in Loanda, the 

 stately capital of Angola, I observed that, although surrounded 

 on its land side by burning sand deserts, the damper places, 

 especially the yards of the houses, were covered during April 

 1854, within a few days, with a gray-green velvety coating, spread 

 like a crust almost uninterruptedly over the level portions of 

 the soil. I looked upon this at first as a vegetation arising 

 from the neighbouring sea-shore, until a subsequent microscopic 

 examination proved, to my great astonishment, that the entire 

 green covering was composed of an immense accumulation of 

 Botrydium,t one of the prettiest little terrestrial algce, which occurs 



* Protococcus atlanticus, Montagne (Note sur un nouveau fait de colorisa- 

 tion des eaux de la mer. Comptes Rend, de I'Acadcmic Sc, 16 Nov. 1846. 



+ This species, occii iring in Loanda, resembles very much in its habitus the 

 Botr. argillaceum, Wall., from which it is distinguished by its brighter colour 

 and closer juxtaposition of the separate vcsicuhv, which are also much smaller 

 than those of the European species. 



