1(52 POUT ST. JULIAN. [CHAP. vin. 



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 Cincin- 

 dela, like lujbrida, a Cyruindis, and a Harpalus, which all live on 

 muddy flats occasionally overflowed by the sea), and one other 

 found dead on the plain, complete the list of the beetles. A good- 

 sized fly (Tabanus) 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 musquitoes 

 on the blood of what animals do these insects commonly 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 accumulated 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 : Pro- 

 fessor 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. J ulian 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 Bio 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, whence 

 the well-rounded pebbles of porphyry have been derived : we may 

 consider its average breath as 200 miles, and its average thickness 

 as about 50 feet. If this great bed of pebbles, without including 

 the mud necessarily derived from their attrition, was piled into a 

 mound, it would form a great mountain chain ! When we consider 

 that all these pebbles, countless as the grains of sand in the desert^ 



