198 Scientific Proceedings, Royal Dublin Society. 



the great erratics lie in and on the shingle belonging to the first pampa 

 level. All the shingle extending from the south and west towards the north 

 and east over the high pampas is one continuous layer, and belongs to the 

 same formation, and may be divided by the line I have indicated into two 

 divisions, a shingle area and a shingle erratic area. This evidence will 

 confirm the view already put forward that the shingle layer belongs to the 

 Ice Age. I have, moreover, carefully examined the erratic boulder area, aird 

 found abundance of scratched stones in it, like those found in the boulder 

 clay of Europe. The limiting line of the erratics probably marks the former 

 termination of a great mass of moving ice, and tlie further extension of the 

 shingle over the plains was possibly due to the action of the multitudinous 

 streams which ran away from the front of this ice-sheet. The chain of the 

 Andes as prolonged through Tierra del Fuego and the islands to the south 

 curves round towards the east in a hook-like manner. The limiting line of 

 the large boulders corresponds in a striking degree with that of the Andes. 

 These facts teird to indicate that during the first Glacial Age the snow and 

 ice which are now limited to the top of the mountains descended some sixty 

 miles into the pampas in the form of a uniform mass, moving outward all 

 the time, and melting away along the line which I have tried to indicate. 

 The ice as it descended ca\ised considerable disruption and erosion of- the 

 mountain tops and hills, and carried with it an immense amount of broken 

 debris, which it deposited on the lower lands ; as the ice melted, the abun- 

 dant streams formed from it carried this material further, rounding off the 

 pebbles as they travelled, and eventually spreading them out over the 

 flattened plains. 



Proceeding to the north from the lower portion of the Eio Coyle, one 

 finds first an area of terraces extending back from the river for distances in 

 different places up to six or even ten miles. About ten miles further across 

 the pampa is another scarp-line, about one hundred and fifty feet high, 

 leading up to another pampa, equally as flat as the one we have just left. 

 The line of this pampa scarp differs from those of the terraces in that it does 

 not run parallel to the river, and it has no corresponding scarp equal to it in 

 height on the south side. It is also much too far back to be connected with 

 the river. After travelling another thirty miles or so northward we come 

 to one more scarp, which brings us on to yet another pampa. Now these 

 two latter pampas, in addition to what I have mentioned, also differ from 

 the terraces, in that they possess all the characteristic flatness which I have 

 alluded to ; in fact, they are pampas just as truly as that wliich we saw north 

 of the Gallegos river. Hence to the north of the Coyle, unlike the same side 

 of the Gallegos river, there are, in addition to the terraces, three distinct 



