Fenton — Physiography and Glacial Geology of 8. Patagonia. 199 



pampas. Now, as we have already seen, the sudden drop from high to low 

 level at the mouth of the Glallegos river probably marks the remains of an 

 old coast-line ; so, taking all the facts into consideration, I am inclined to 

 believe that these latter steps belong to the pre-shingle period, and are 

 remains of old coast-lines also. They were formed well back in tertiary 

 times, when the high winds and dry climate prevailed, and they show a 

 steady tendency towards elevation of the land, which, however, was inter- 

 mittent in its action. Passing now along the north side of the Gallegos 

 river, towards the west, we find that, sixty miles from the coast, the typical 

 pampa still exists in all its flatness, even up to the very edges of the deep 

 canadones. Another fifteen miles, however, brings about a complete change ; 

 here the country begins to rise suddenly fifty to a hundred feet or so, and 

 then goes on for another sixty miles before it reaches the mountains. The 

 surface of this latter portion is completely changed from the pampas below, 

 in that the flatness disappears and an undulatory condition takes its place. 

 In addition, however, great stones appear here also; in fact, we find that this 

 sudden rise in the level of the pampa marks the line I have already indicated 

 as the termination of the erratic boulders. This line of junction between 

 the flat pampa and the undulatory land is as a rule clear to the north of the 

 Gallegos river, and one can trace it without much difficulty. To the south 

 of the river, however, it is not so clear, as two actions have apparently come 

 into play since the great shingle period which have complicated matters : 

 one of these is the elevation of the southern coast-line, and the other is the 

 enormous erosive action of the great river floods. The boulder shingle 

 deposit is, undoubtedly, of glacial origin ; and here it would seem that the 

 great undulatory boulder area, the shingle of which runs up to a hundred 

 feet in thickness, is really the remains of a great terminal moraine, and that 

 it marks the limit of the advance of the ice during the first great ice stage. 



IV. 



The Recent Volcanic Series. 



About eighteen miles to the west of the port of Gallegos on the north 

 bank of the river, we find the first evidence of former volcanic activity, and 

 from this point for over a hundred miles in a westerly and south-westerly 

 direction many extensive sheets of lava are to be found spread out over the 

 surface of the plains. There is no very large volcano in this portion of the 

 country ; but the number of small cones is immense, and they can be seen 

 dotted all over the pampas as far as one's eye can reach from horizon to 

 horizon. This lava must have resulted from successive eruptions, occurring 



