364 Pampean Formation : pakt n. 



Society, as tliey would be of considerable service to any 

 one investigating the geology of that country. The 

 Pampean formation is in several respects so interesting, 

 from containing an extraordinary number of the remains 

 of various extinct Mammifers, such as Megatherium, 

 Myloclon, Mastodon, Toxodon, &c, and from its great 

 extent, stretching in a north and south line for at least 

 750 geographical miles, and covering an area fully 

 equal to that of France, that, as it appears to me, a 

 record ought to be preserved of these borings. South- 

 ward, at the Eio Colorado, the Pampean formation 

 meets the great Tertiary formation of Patagonia ; and 

 northward, at St. Fe Bajada, it overlies this same for- 

 mation with its several extinct shells. 



In the central region near Buenos Ayres no natural 

 section shows its thickness ; but, by the borings there 

 made in two artesian wells (figs. 31 and 32), the Pampean 

 mud, with tosca-rock, is seen to extend downwards 

 from the level of the Rio .Plata to a depth of sixty-one 

 feet, and to this must be added fifty-five feet above 

 the level of the river. These argillaceous beds overlie 

 coarse sand, containing the Azara labiata, (a shell 

 characteristic of the Pampean formation), and attaining 

 a thickness of about ninety-three feet. 1 So that the 



1 The following extract from the Eeport of the borers relates to 

 this bed : — The bed of yellow, fluid sands between 18 m, 60 and 47 m, 20 

 below the ground 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 cur- 

 rent (' overflowing 1 ), was 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 rirst overflowing current. The great spring was met with at 

 77 m -6o.' 



As regards the quality and abundance of the water, Mf\ Coghlan 

 remarks that ' The quantity of water discharged per hour through a 

 tube of about 4£ inches in diameter, at a level of 6 feet above high- 



