Fenton — Recent Pampa and other Formations in Paiagonia. 605 



When the great ice-sheet had receded and the climate had assumed a 

 milder type, there occurred a prolonged period of great volcanic activity, and 

 there were in places several outpourings having considerable periods between 

 them. There are in some places hundreds of feet of accumulated debris 

 between the successive sheets of basalt, and also in some places the basalt has 

 a much more aged and worn appearance than in others. Hence the out- 

 pourings probably lasted for many thousands of years. Then occui-red a 

 period of slow upheaval, more marked towards the west, with great accumu- 

 lation of snow and ice on the high ground, melting, however, as it reached 

 the plains and forming large and rapid rivers with considerable eroding 

 power. In some places small glaciers descended into the river valleys for a 

 certain distance, as is shown by the occurrence of the striated basalt boulders 

 mentioned on p. 603 ; but none of them reached as far as the Atlantic coast. 

 The ice action in this case was small and limited : it extended from the high 

 lands to the west towards the Atlantic, it was purely local, and was probably 

 not part of a general lee Period. This condition must have lasted for a very 

 long time, if we estimate it in thousands of years, as we have seen that it was 

 sufficient to cut a river-valley two miles wide through hundreds of feet of 

 hard basalt and upwards of a thousand feet of Pampa formation. In turn 

 there followed a period of subsidence and quiescence, when the snow re- 

 ceded to the tops of the mountains and the pampas were left bare and dry. 

 The subsidence continued until a good part of the southern pampas of the 

 continent were under the sea, but only for a short while, after which elevation 

 began again, and is still going on. As evidence of recent subsidence under 

 the sea a number of salt lakes are found all over the pampas, and a consider- 

 able amount of salt is found in the soil everywhere on the surface. It is well 

 known that where water stands for any length of time in superficial wells it 

 becomes perceptibly salt. Recent sea-shells have also been found in the bed 

 of some of the canadones to a height of hundreds of feet above the sea-level. 

 In the Grallegos River, slightly above the town, the bed-rock of the surrounding 

 Santa Cruz formation appears on the surface over extensive areas at low 

 water, washed and swept clean of mud. Now, if the river-bed were sinking, 

 we should expect to find nothing but mud, sand, and shingle all over from 

 side to side ; but if it were rising, we should expect to fiud such mud and 

 shingle in most places swept off to sea, and the rock becoming 

 eroded away. The latter is exactly what is found. Also, the small island 

 in San Julian Bay, where Drake was supposed to have executed some of his 

 mutineers about 300 years ago, which was then only a few feet above sea- 

 level, is still at about the same level, notwithstanding the constant planing 

 down action it is subjected to by the strong winds which blow there. These 



