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 iiead 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 multitud.e 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 8 00 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, 



