1834.] GEOLOGY OF PATAGONIA. 163 



have been derived from the slow falling of masses of rock on the 

 old coast-lines 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 beds, and 

 long subsequently to the underlying 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 Patagonia 

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

 now existing 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, 

 forming at successive levels the long lines of cliffs or escarpments, 

 which separate the different plains as they rise like steps one 

 behind the other. The elevatory movement, and the eating-back 

 power of the sea during the periods of rest, Lave been equable over 

 long lines of coast ; for I was astonished to find that the step-like 

 plains stand at nearly corresponding heights at far distant points. 

 The lowest plain is 90 feet high ; and the highest, which 1 ascended 

 near the coast, is 950 feet ; and of this, only relics are left in the 

 form of flat gravel-capped hills. The upper plain of Santa Cruz 

 slopes up to a height of 3000 feet at the foot of the Cordillera. I 

 have said that within the period of existing sea-shells Patagonia has 

 been upraised 300 to 400 feet : I may add, that within the period 

 when icebergs transported boulders over the upper plain of Santa 

 Cruz, the elevation has been at least 1500 feet. Nor has Patagonia 

 been affected only by upward movements: the extinct tertiary 

 shells from Port St. Julian and Santa Cruz cannot have lived, 

 according to Professor E. Forbes, in a greater depth of water than 

 from 40 to 250 feet ; but they are now covered with sea-deposited 

 strata from 800 to 1000 feet in thickness : hence the bed of the sea, 

 on which these shells once lived, must have sunk downwards 

 several hundred feet, to allow of the accumulation of the super- 

 incumbent strata. What a history of geological changes does the 

 simply-constructed coast of Patagonia reveal ! 



