182 ON THE ORIGIN OF COAL. 



upraising period has been interrupted by at least 

 eight long periods of rest, during which, the sea 

 ate deeply back into the land, forming, at succes- 

 sive levels, the long line 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, have been equable 

 over long lines of coast ; for 1 was astonished to 

 find that the step-like plains stand at nearly cor- 

 responding heights, at far distant points. The 

 lowest plain is ninety feet] high, and the highest 

 which I ascended, near the coast, is nine hundred 

 and fifty 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 three 

 thousand feet, at the foot of the Cordillera. I 

 have said, that within the period of existing sea 

 shells, Patagonia has been upraised three hundred 

 to four hundred 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 fifteen hundred feet. Nor has Pata- 

 gonia 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. 



