My intelligent correspondent Dr. Redhead, who has lived for more than a quarter of a century in the upper provinces, and to whom I am indebted for some of the most valuable of my information respecting them, speaking of its geological appearance, observes in one of his letters how forcibly he had been led to conjecture that the southern part of the province of Santiago must once have been a sea-coast. "Its sandy hillocks, he says, always reminded him of those on the shores of Flanders:"--certain it is, that throughout the whole extent of this sandy zone, from Ambargasta to Noria, the level of the country becomes very much depressed, and falls very nearly to that of Buenos Ayres; thus in the very heart of the continent, at a distance of 700 miles direct from the sea, we have a considerable tract of land hardly elevated above its immediate shores. The following table of barometrical observations, taken by Dr. Redhead, will not only show the variations in the height of the country intervening between Buenos Ayres and Santiago, but also of that to the northward, along the high road, as far as Tupiza in Peru:-- Barometrical Observations, made on the road from Buenos Ayres to Potosi, by Dr. Redhead:-- +---------+---------------------+---------+-------+--------+-------+ |Distance | | | | | | |from one | | | | | | |place to | | | | | | |another |Point of Observation |Barometer|Thermo-| Date | Hour | | | | | meter | | | |Post | | | | | | |leagues | | | | | | +---------+---------------------+---------+-------+--------+-------+ | 134 |Rio Tercero from } | | | | | | | Buenos Ayres } | 28·945 | 86 |Feb. 11 |11 a.m.| | 3 |Cordova | 28·400 | 86 | 20 | 4 p.m.| | 14 |Sin-Sacate | 27·990 | 75 |Mar. 12 |11 a.m.| | 22 |San Pedro | 26·990 | 60 | 17 | 6 a.m.| | 4 |Durasno | 27·300 | 73 | -- | 9 a.m.| | 4 |Piedritas | 27·500 | 72 | -- | Noon. | | 4 |Pozo del Tigre | 27·550 | 71 | -- | 5 p.m.| | 6 |Portezuela | 27·860 | 69 | 18 | Noon | | 6 |Ambargasta } | 28·875 | 67 | 19 | 9 a.m.| | 6 |Punta del Monte} The | 29·260 | 82 | -- | 4 p.m.| | 6 |Salinas } Travesia| 29·600 | 68 | 20 | 6 a.m.| | 14 |Noria } | 29·400 | 76 | -- | 2 p.m.| | 24 |Santiago del Estero | | | | | | 40 |Tucuman | 27·563 | 75 |Feb. 10 | | | 100 |Jujuy | | | | |