604 Scientific Proceedings^ Royal Dublin Society. 



they are found on the sides and summits of the hills on either side up to 

 over 1000 feet ahove the sea-level, just as well as in the valley, except that 

 in the latter situation they are congregated more closely. 



In all the parts of the country visited by the writer, to the north of a lino 

 presently to be mentioned, no large erratics are found on the surface of the 

 pampa, although there are abundant outpourings of volcanic matter right 

 away to the north of the Santa Cruz Eiver. 



On drawing a line through southern Patagonia on the Argentine side, 

 from a point on the Atlantic coast about twelve miles north of the 52nd 

 parallel of latitude, due west to a point about twelve miles to the eastward of 

 the 71st meridian west of Grreenwich, and then curving slightly to the 

 northward, one would more or less mark the northern limit of the large 

 erratic boulders. Boulders are found to the north of this line, but they are 

 all small and more or less rounded. 



Now, from the facts before us the writer would suggest that we have 

 evidence of two post-pampean Ice Periods in southern Patagonia — one large 

 or general and one small or local. The large or general occurred first and 

 was part of a huge glaciation extending from the south or south-west. It 

 occurred after the pampas were formed, since we find everywhere the huge 

 boulders lying on the surface. Its northern range was limited by the line 

 which I have mentioned, and it may have been an extension to the north of 

 the great Antarctic Ice Barrier, carrying boulders with it from the continent 

 that lies around the south polar regions. These boulders may also have been 

 carried by floating ice, but this hypothesis would necessitate great sub- 

 mergence, as some of the boulders which the writer has seen are as large as a 

 small house, and must weigh almost hundreds of tons, and the icebergs which 

 carried them would have had to be of colossal dimensions. Moreover, another 

 point is that the largest boulders are often found on the highest portions of 

 the pampa, in places up to two thousand feet above the sea-level. Accepting 

 the hypothesis of a great Ice Period, we come to the question of its time, and 

 the writer suggests that it was probably of late Pliocene or early Pleistocene 

 Age, his reason being as follows : — Mr. J. B. Hatcher has pointed out that 

 there is a gradual dip from north to south in the formations of southern 

 Patagonia along the east or Atlantic border. Now, about Cape Fairweather 

 is a considerably worn marine formation which would seem to be of Pliocene 

 origin, as it lies unconformably on the Santa Cruz formation, which is 

 terrestrial, and has been provisionally classed as Miocene. This would place 

 the Pampa formation to the south, the dip still continuing, either in late 

 Pliocene or Pleistocene, aud it is on the surface of this formation that the 

 great boulders are fouud. 



