Fenton — Physiography and Glacial Geology of S. Patagonia. 215 



a few feet below the main level ; these may vary from a hundred yards or 

 so up to four or five hundred in breadth, and are covered by short, fine grass. 

 They have often in their centres patches of bare shingle, and no bush is found 

 growing in any portion of them. These patches mark the sites of spring 

 lagoons, and their semi-bareness is due to the partial sterilization of the 

 surface produced by the water, which lies on them at times for some months. 

 These spring lagoons are only formed after severe winters, when there is 

 heavy snow, and sometimes they are absent for a period of six or seven 

 years. From this it would seem that we meet all grades of bajos, from the 

 merest shallow semi-bare patches, only a few feet below the level of the 

 main pampa, down to great hollows several leagues in length and hundreds 

 of feet in depth. On the floor of some of these bajos we find a class of hill 

 which rises abruptly in the west and falls gradually towards the east. These 

 hills, of which there are a number in some bajos, are capped with a thin 

 layer of shingle, and their tops would seem to mark a former horizon in the 

 formation of the valley. Bajos are found, not only on the main pampa, but 

 on all the lower horizons, except the floors of the river-valleys. On the side 

 of a bajo situated on the third terrace above the floor of the Coyle valley 

 is a very well-marked terrace about sixty feet above the lagoon, which was, 

 at the time of my visit, of pure salt; its top is as flat and its edge is as 

 clean cut as any of those found on the sides of the river valleys. 

 Barometrical reading showed the surface of the lagoon in the bajo to be only 

 twenty feet above the Coyle river. 



It has been suggested that these bajos probably originated through a 

 combination of wind and water action. The water remains in a slight 

 hollow for a few mouths after the melting of the snow in the spring, and 

 causes destruction of the vegetation which normally protects the surface. 

 The soil beneath is thereby exposed, so that, when the water has dried up, 

 tlie winds, which blow very strongly in summer, attack it, eat into it, and 

 blow it away. The next season the lagoon is a little larger, more vegetation 

 is destroyed, more earth is blown out, and the hollow becomes deeper. This 

 goes on year after year until a huge bajo is formed. This explanation is 

 very plausible, and seems to agree with the facts in many instances ; in fact, 

 I may say that I have seen in more than one place this mode of action actually 

 working. Tor instance, near the town of Gallegos at least two such places 

 occur, where the dust and sand of the hollows is found to be heaped up on 

 the eastern sides in the form of mounds. I also know one small bajo on the 

 high pampa between Gallegos and Coyle where such a mound can be seen 

 on the east side of the hollow. In the vast majority of instances, however, 

 no mounds or elevations can be seen on the sides of the bajos, and no 

 scooping out seems to be occurring to-day. 



