IN THE WAKE OF THE “ CHALLENGER.’ 
15 
On Friday evening', July 4, the Challenger arrived at Porta 
Delgada, the capital of the island of San Miguel, one of the 
easternmost of the Azores group. At Furnas, in San Mi- 
guel, there are two sets of boiling springs which were explored 
by the botanist of the expedition for algae. Connected with 
one spring there is a basin full of intensely hot water always in 
ebullition. This had no algae in it. Some diatoms were found 
in a hot sulphureous spring, probably derived from a cool spring 
which mingled with it. Certain Oscillatorioe were also dis- 
covered in water so hot as to scald the hand. Unfortunately no 
exact record of temperature could be made, as no thermometers 
were at hand which registered sufficiently high.* A peculiar 
substance of the consistence of Indiarubber was found floating 
on one of the hot-springs. It burnt like the substance which 
it counterfeited, and in doing so emitted a similar smell. It 
resembled, too, as far as Mr. Moseley could remember, a pecu- 
liar elastic substance, a specimen of which is in the Kew her- 
barium among the lichens found upon the shores of an Austra- 
lian lake. By some it has been held to be a mineral, and on 
this assumption some specimens are under Professor Maskelyne’s 
care, in the British Museum. 
The Challenger left the Azores for the Cape de Verde Islands 
on Wednesday, July 9. The Island of St. Vincent, one of the 
principal of the group, was visited. It has a flat central tract 
surrounded by high land, the former part being evidently the 
bottom of an ancient crater. The abundant plant is Lavandula 
rotundifolia. The tomato (introduced) has run wild every- 
where. At the time of the visit there had been no rain for a 
year, but the island is said to become green after rain as if by 
magic. The rocks about tide-mark are covered with a band of 
incrustation composed of calcareous algae. This incrustation is 
of several colours, white, pink, or cream-colour. 
At St. Paul’s Rocks, as at St. Vincent, there is a pinkish in- 
crustation about tide-mark upon the rocks. f A green alga, 
which is constantly being loosened by the surf from the bottom, 
and floats upon the surface, is gathered by the 66 noddies ” 
(Sterna stolida ) for building their nests, but is not used by the 
“ boobies ” ( Sula fusca). A few bushels of guano are to be 
found in rock-hollows, which is almost wholly soluble in nitric 
acid ; but no diatoms — which abound in Peruvian guano — are 
* For some remarks by Mr. Archer on these algae, &c., see “ Journ. Linn. 
Soc. Botany,” vol. xiv. p. 328. 
t Darwin, in his “Naturalist's Voyage,” mentions that there is a similar 
incrustation on the coast of Ascension, resembling certain cryptogamic 
plants ( Marchantice ) often seen on damp walls. Of this he gives a beautiful 
woodcut. 
