i8o 
PORT ST. JULIAN 
CHAP. 
cubes ! We attributed our extreme thirst to the dryness of the 
atmosphere ; but whatever the cause might be, we were exceed¬ 
ingly glad late in the evening to get back to the boats. Although 
we could nowhere find, during our whole visit, a single drop of 
fresh water, yet some must exist; for by an odd chance I found 
on the surface of the salt water, near the head of the bay, a 
Colymbetes not quite dead, which must have lived in some not 
far distant pool. Three other insects (a Cincindela, like hybrida ,, 
a Cymindis, and a Harpalus, which all live on muddy flats occa¬ 
sionally overflowed by the sea), and one other found dead on 
the plain, complete the list of the beetles. A good-sized fly (Ta- 
banus) was extremely numerous, and tormented us by its painful 
bite. The common horsefly, which is so troublesome in the 
shady lanes of England, belongs to this same genus. We here 
have the puzzle that so frequently occurs in the case of mus- 
quitoes—on the blood of what animals do these insects com¬ 
monly feed ? The guanaco is nearly the only warm-blooded 
quadruped, and it is found in quite inconsiderable numbers 
compared with the multitude of flies. 
The geology of Patagonia is interesting. Differently from 
Europe, where the tertiary formations appear to have accu¬ 
mulated in bays, here along hundreds of miles of coast we have 
one great deposit, including many tertiary shells, all apparently 
extinct. The most common shell is a massive gigantic oyster, 
sometimes even a foot in diameter. These beds are covered by 
others of a peculiar soft white stone, including much gypsum, 
and resembling chalk, but really of a pumiceous nature. It is 
highly remarkable, from being composed, to at least one-tenth 
part of its bulk, of Infusoria : Professor Ehrenberg has already 
ascertained in it thirty oceanic forms. This bed extends for 500 
miles along the coast, and probably for a considerably greater 
distance. At Port St. Julian its thickness is more than 800 feet ! 
These white beds are everywhere capped by a mass of gravel, 
forming probably one of the largest beds of shingle in the 
world : it certainly extends from near the Rio Colorado to 
between 600 and 700 nautical miles southward ; at Santa Cruz 
(a river a little south of St. Julian) it reaches to the foot of the 
Cordillera ; half-way up the river its thickness is more than 
200 feet; it probably everywhere extends to this great chain,. 
