344 Pampean Formation. pakt ii. 



where tlie Parana makes a remarkable bend, M. 

 Bonpland found some singular amygdaloidal rocks, 

 which perhaps may belong to this same epoch. I may 

 remark that, judging from the size and well-rounded 

 condition of the blocks of rock in the above-described 

 conglomerates, masses of primary formation probably 

 existed at this tertiary period above water : there is, 

 also, according to M. Isabelle, much conglomerate- 

 farther north, at Salto. 



From whatever source and through whatever means 

 the great Pampean formation originated, we here have, 

 I must repeat, unequivocal evidence of a similar 

 action at a period before that of the deposition of the 

 marine tertiary strata with extinct shells, at St. Fe and 

 P. Gorda. During also the deposition of these strata, 

 we have, in the intercalated layers of red Pampean-like 

 mud and tosca-rock, and in the passage near S. Juan of 

 the semi-crystalline limestones with agate into tosca 

 undistinguishable from that of the Pampas, evidence 

 of the same action, though continued only at intervals 

 and in a feeble manner. We have further seen that in 

 this district, at a period not only subsequent to the de- 

 position of the tertiary strata, but to their upheavement 

 and most extensive denudation, true Pampean mud 

 with its usual characters and including mammiferous 

 remains, were deposited round and between the hills 

 or islets formed of these tertiary strata, and over the 

 whole eastern and low primary districts of Banda 

 Oriental. 



Earthy mass, with extinct mammiferous remains, 

 over the porphyritic gravel at S. Julian, lot. 49° 14' 

 8. in Patagonia. — This case, though not coming 

 strictly under the Pampean formation, may be con- 

 veniently" given here. On the south side of the 

 harbour, there is a nearly level plain (mentioned in 



