34-0 Pampean Formation. pake n. 



they contain about seven per cent, of animal matter, 

 and eight per cent, of water. 1 



The older tertiary strata, forming the higher isolated 

 hills and extensive tracts of country, vary, as I have 

 said, extraordinarily in composition : within the dis- 

 tance of a few miles, I sometimes passed over crystalline 

 limestone with agate, calcareous tuffs, and marly rocks, 

 all passing into each other, — red and pale mud with 

 concretions of tosca-rock, quite like the Pampean for- 

 mation, — calcareous conglomerates and sandstones, — 

 bright red sandstones passing either into red con- 

 glomerate, or into white sandstone, — hard siliceous 

 sandstones, jaspery and chalcedonic rocks, and numerous 

 other subordinate varieties. I was unable to make out 

 the relations of all these strata, and will describe only 

 a few distinct sections : — in the cliffs between P. Gorda 

 on the Uruguay and the A. de Vivoras, the upper bed 

 is crystalline cellular limestone often passing into cal- 

 careous sandstone, with impressions of some of the same 

 shells as at St. Fe Bajada ; at P. Gorda, 2 this limestone 

 is interstratified with, and rests on, white sand, which 

 covers a bed about thirty feet thick of pale-coloured 

 clay, with many shells of the great Ostrea Patagonica : 

 beneath this, in the vertical cliff, nearly on a level with 

 the river, there is a bed of red mud absolutely like the 

 Pampean deposit, with numerous often large concre- 

 tions of perfectly characterised white, compact tosca- 

 rock. At the mouth of the Vivoras, the river flows 

 over a pale cavernous tosca-rock, quite like that in the 



1 Liebig (' Chemistry of Agriculture,' p. 191) states that fresh 

 dry bones contain from thirty-two to thirty-three per cent, of dry 

 gelatine. See also Dr. Daubeny in ' Edin. New Phil. Journ.' vol. 

 xxxvii. p. 293. 



2 In my ' Journal ' (p. 171, 1st edit.), I have hastily and inaccu- 

 rately stated that the Pampean mud, which is found over the eastern 

 part of B. Oriental, lies over the limestone at P. Gorda ; I should 

 have said that there was reason to infer that it was a subsequent or 

 superior deposit. 



