2 1 8 Summary of Results. paet n. 



of rest and denudation, we can understand the pebbles 

 being of about the same size over the entire width of 

 the step-like plains, — the occasional thin covering of 

 sandy earth, — and the presence of broken, unrolled 

 fragments of those shells, which now live exclusively 

 near the coast. 



Summary of Results. — It may be concluded that 

 the coast on this side the continent, for a space of at 

 least 1,180 miles, has been elevated to a height of 100 

 feet in La Plata, and of 400 feet in Southern Patagonia, 

 within the period of existing shells, but not of existing 

 mammifers. That in La Plata the elevation has been 

 very slowly effected : that in Patagonia the movement 

 may have been by considerable starts, but much more 

 probably slow and quiet. In either case, there have 

 been long intervening periods of comparative rest, 1 

 during which the sea corroded deeply, as it is still cor- 

 roding, into the land. That the periods of denudation 

 and elevation were contemporaneous and equable over 

 great spaces of coast, as shown by the equable heights 

 of the plains ; that there have been at least eight 

 periods of denudation, and that the land, up to a height 

 of from 950 to 1,200 feet, has been similarly modelled 

 and affected : that the area elevated, in the southern- 

 most part of the continent, extended in breadth to 

 the Cordillera, and probably seaward to the Falkland 

 Islands ; that northward, in La Plata, the breadth is 

 unknown, there having been probably more than one 

 axis of elevation ; and finally, that, anterior to the 

 elevation attested by these upraised shells, the land was 

 divided by a Strait where the river Santa Cruz now 



1 I say comparative and not absolute rest, because the sea acts, 

 as we have seen, with great denuding power on this whole line of 

 coast ; and therefore, during an elevation of the land, if excessively 

 slow (and of course during a subsidence of the land), it is quite 

 possible that lines of cliff might be formed. ** 



