186 



CHARLES DARWIN 



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 suc- 

 cessive 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 

 ppwer of the sea during the periods of rest, have 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 I ascended near the cpast, is 

 950 feet; and of this, only relics are left in the form of fiat 

 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, Pata- 

 gonia 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 superincum- 

 bent strata. What a history of geological changes does the 

 simply-constructed coast of Patagonia reveal ! 



At Port St. Julian, 12 in some red mud capping the gravel 

 on the 90-feet plain, I found half the skeleton of the Macrau- 

 chenia Patachonica, a remarkable quadruped, full as large as 

 a camel. It belongs to the same division of the Pachy- 

 dermata with the rhinoceros, tapir, and palaeotherium ; but 

 in the structure of the bones of its long neck it shows a clear 

 relation to the camel, or rather to the guanaco and llama. 

 From recent sea-shells being found on two of the higher 



12 I have lately heard that Capt. Sulivan, R.N., has found numerous fossil 

 bones, embedded in regular strata, on the banks of the R. Gallegos, in lat. 

 51 0 4'. Some of the bones are large; others are small, and appear to have 

 belonged to an armadillo. This is a most interesting and important discovery. 



