72 GEOLOGY OF PATAGONIA. [chap, viil 



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 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 coast, is 950 feet ; 

 and of this, only relics are left in the form of flat gravel- 

 capped hills. The upper plain of S. 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 up- 

 raised 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 s-ea-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 accu- 

 mulation of the superincumbent strata. What a history of geo- 

 logical changes does the simply-constructed coast of Patagonia 

 reveal ! 



At Port St. Julian *, 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 Pachydermata 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 step-formed plains, which must have 

 been modelled and upraised before the mud was deposited in 

 which the Macrauchenia was intombed, it is certain that this 

 curious quadruped lived long after the sea was inhabited by its 



* 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° 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 djs- 

 •overy, 



