322 Pampean Formation. paet n. 



brackish-water origin, hereafter to be mentioned, from 

 a central point in the Pampean formation. In these 

 two beds, especially in the lower one, bones of extinct 

 mammifers, some embedded in their proper relative 

 positions and others single, are very numerous in a small 

 extent of the cliffs. These remains consist of, first, 

 the head of Ctenomys antiqmis, allied to the living 

 C. Brasiliensis ; secondly, a fragment of the remains 

 of a rodent ; thirdly, molar teeth and other bones of a 

 large rodent, closely allied to, but distinct from, the 

 existing species of Hydrochcerus, and therefore probably 

 an inhabitant of fresh water ; fourth and fifthly, portions 

 of vertebrae, limbs, ribs, and other bones of two rodents; 

 sixthly, bones of the extremities of some great mega- 

 theroid quadruped. 1 The number of the remains of 

 rodents gives to this collection a peculiar character, 

 compared with those found in any other locality. All 

 these bones are compact and heavy ; many of them are 

 stained red, with their surfaces polished; some of the 

 smaller ones are as black as jet. 



Monte Hermoso is between fifty and sixty miles 

 distant in a SE. line from the Yentana, with the inter- 

 mediate country gently rising towards it, and all con- 

 sisting of the Pampean formation. "VYhat relation, 

 then, do these beds, at the level of the sea and under 

 it, bear to those on the flanks of the Yentana, at the 

 height of 840 feet, and on the flanks of the other 

 neighbouring sierras, which, from the reasons already 

 assigned, do not appear to owe their greater height to 

 unequal elevation ? When the tosca-rock was accumu- 

 lating round the Yentana, and when, with the exception 

 of a few small rugged primary islands, the whole wide 



1 See 'Fossil Mammalia.' (p. 109), by Professor Owen, in the 

 * Zoology of the Voyage of the Beagle : ' and Catalogue (p. 36) of 

 ' Fossil Remains in Museum of Royal College of Surgeons. 5 



