70 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Dec. 3, 



of the great estuarine or Pampean formation near Buenos Ayres is 

 nearly 210 feet. 



Fig. 2. — Detailed Section of the Artesian Well at Barracas. 



Thickness 

 in metres. 



a. Sand 4'33 



b. Very arenaceous clay 8 - 02 



fFineclay 1-05 



°' \ Blue plastic clay 2-90 



d. Tosca with calcareous nodules 230 



e. Yellow sand, very fine and fluid, with quartz- 

 pebbles and fluviatile shells 28'60 



/. Green clay, more or less plastic and calcareous, 

 with iron-pyrites, marine shells, and nodules 



of lithographic stone 20*30 



g. Green sand, with shells and quartz -pebbles '80 



k. Shelly limestone "45 



i. Calcareous clay 2*00 



Jc. Shelly sandstone -25 



/. Green arenaceous clay 2*00 



m. Shelly sandstone -30 



n. Speckled sand -70 



o. Very compact arenaceous clay 2*25 



p. Coarse sandstone 140 



q. Green sand, very fine and fluid, with quartz- 

 pebbles and shells 2*35 



This formation rests on various marine beds of indurated green 

 clay, sand with corals, sandstone, and limestone, altogether 107 feet 

 in thickness. These beds contain fragments of the great Ostrea 

 Patagonica, 0. Alvarezii (?), Pecten Paranensis, and other shells, 

 apparently the same (but they have not been rigorously compared) 

 with those enumerated by M. A. d'Orbigny and by myself as found 

 at Sta. Pe Bajada, as well as at various points on the coast of Pata- 

 gonia. The already enormous continuous extension of the Pata- 

 gonian Tertiary formation is thus largely increased. Beneath these 

 beds a mass of red calcareous clay, becoming in the lower part more 

 and more marly, containing layers of sand, and of the thickness of 

 213 feet, was bored through to a depth of 470 feet from the level of 



contains a subterranean ascending current, the level of which has not varied by 

 a centimetre for three years. The level is m, 60 (2 feet over the level of the 

 wells at Barracas). This bed ('napa') is powerfully absorbent. At 68 m, 30 a 

 second subterranean current ('overflowing') w r as met, which rose one foot 

 over the surface of the ground at Barracas. The discharge was about 50 pipes 

 daily, but the water was salt and undrinkable. At 73 m, 30 was found a third 

 subterranean current ('overflowing'), which reached with difficulty the level 

 of the ground. The discharge might be calculated at 100 pipes daily. The 

 water was very salt, and absorbed that of the first overflowing current. The 

 great spring was met with at 77 m, 65." 



As regards the quality and abundance of the water, Mr. Coghlan remarks that 

 " The quantity of water discharged per hour through a tube of about 4-i- inches in 

 diameter, at a level of 6 feet above high-water mark, was 2658 gallons. Its tem- 

 perature was 21° Cent., and it had a slightly disagreeable taste, from its being 

 impregnated with salts of lime and magnesia and a small quantity of sulphu- 

 ret ted hy drogen .' ' 



