328 Pampean Formation. past n. 



gether, as did some ribs and the bones of a leg, that I 

 thought that they must originally have belonged to two 

 skeletons, and not have been washed in single ; but as 

 remains were here very numerous, I will not lay much 

 stress on these two cases. We have just seen that the 

 armour of the Dasypoid quadruped was certainly em- 

 bedded together with some of the bones of the feet. 



Professor Ehrenberg l has examined for me speci- 

 mens of the finer matter from in contact with these 

 mammiferous remains : he finds in them two Polygas- 

 trica, decidedly marine forms ; and six Phytolitharia, 

 of which one is probably marine, and the others either 

 of fresh-water or terrestrial origin. Only one of these 

 eight microscopical bodies is common to the nine from 

 Monte Hermoso : but five of them are in common with 

 those from the Pampean mud on the banks of the 

 Parana. The presence of any fresh-water Infusoria, 

 considering the aridity of the surrounding country, is 

 here remarkable : the most probable explanation appears 

 to be, that these microscopical organisms were washed 

 out of the adjoining great Pampean formation during 

 its denudation, and afterwards redeposited. 



We will now see what conclusions may be drawn 

 from the facts above detailed. It is certain that the 

 gravel-beds and intermediate red mud were deposited 

 within the period, when existing species of Mollusca 

 held to each other nearly the same relative proportions 



1 ' Monatsberichten der konig. Akacl. zu Berlin,' April, 1845. The 

 list consists of, — 



POLYGA.STEICA. 

 Gallionella sulcata. | Stauropteraaspera? fragm, 



Phytolithakia. 

 Lithasteriscustuberculatus. I Spongolithis acicularis 



Lithostylidium Clepsammidium. 

 „ quadratum. 



„ rude. 



,, unidentatum. 



