SECOND JOURNEY INTO THE INTERIOR. 163 



a lofty, basalt-capped table land, which extended uninterruptedly for a 

 distance of forty miles. At the southern end this basaltic platform had 

 an elevation of one thousand feet or more above the valley, but at its 

 northern extremity the difference in elevation was scarcely more than two 

 hundred feet. On the east of the valley lay the great lava fields, which 

 in this region cover most of the interior of the Patagonian plains. From 

 certain patches of green in the vegetation, discernible at none too frequent 

 intervals just below the basaltic platform on our west, we knew that water 

 for ourselves and horses could be had, if we kept along the base of this 

 escarpment. We, therefore, crossed the valley to a point just beneath the 

 first of these "mananteals," believing not only that we should find an 

 abundance of water for our purposes, but also that the surface of the valley 

 at the foot of the cliff would afford us a convenient highway for our 

 journey northward. In the first of these suppositions we were not dis- 

 appointed, but we were quite mistaken as to the latter, for instead of the 

 valley continuing as an unbroken and level surface to the foot of the bluff, 

 as we had supposed, it was interrupted throughout the entire extent of the 

 latter by a series of deep depressions, usually from one to two or three miles 

 in diameter and frequently several hundred feet in depth. These depres- 

 sions were quite similar to those occupied by the salt lagoons already 

 mentioned as existing throughout the eastern plains region. They were 

 usually separated from one another by a narrow isthmus extending from 

 the level plain to the foot of the bluff. The bluffs surrounding these 

 depressions were, for the most part, rather precipitous and not easy 

 of descent and ascent with our wagon, so that we had usually to 

 keep to the eastward of them as we proceeded on our journey. The 

 origin of many of these depressions, or "sink holes," was a question to 

 which I gave much attention while in Patagonia, but was never able to 

 arrive at any very satisfactory conclusion. They will be more fully dis- 

 cussed when treating of the geography and geology of this region. There 

 was an abundance of water at all the mananteals, though it was only to 

 be reached by a long and laborious climb for several hundred feet up the 

 steep incline, covered over with huge blocks of lava derived from the 

 basaltic platform at the summit The fauna and flora in and about the 

 springs of these mananteals were quite varied and differed exceedingly 

 from those of the surrounding country. They afforded most excellent 

 collecting grounds, and at our first camp we remained for several days to 



