1834.1 GEOLOGY OF PATAGONIA. 17j 



Bometinies 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 ha*; 

 already ascertained in it tliirty oceanic forms. This bed extends 

 for 500 miles along the coast, and probably for a considerably 

 srreater 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 Eio Colorado to be- 

 tween 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 breadth as 200 miles, and its average 

 thickness as about 50 feet. If this great bed of pebbles, with- 

 out 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, have been derived from the slow falling of 

 masses of rock on tlie old coast-linee and banks of rivers ; and 

 that these fragments have been dashed into smaller pieces, and 

 that each of them has since been slowly rolled, rounded, and 

 far transported, the mind is stupified in thinking over the long, 

 absolutely necessary, lapse of years. Yet all this gravel has 

 been transported, and probably rounded, subsequently to the 

 deposition of the white betls, and long subsequently to the under- 

 lying beds with the tertiary shells. 



Everything in this southern continent has been effected on a 

 grand scale : the land, from the Rio Plata to Tierra del Fuego, 

 a distance of 1200 miles, has been raised in mass (and in Pata- 

 gonia to a height of between 300 and 400 feet), within the period 

 of the now existins;' sea-shells. The old and weathered shells 

 left on the surface of the upraised plain still partially retain 

 their colours. The uprising movement has been interrupted by 

 at least eight long periods of rest, during which the sea ate deeply 

 back into the land,forn\ing at successive levels the long lines of 



