3*3 



CHAPTER XI. 



ON THE FORMATIONS OF THE PAMPAS. 



'Miner alogical constitution — Microscopical structure — Buenos Ayres, 

 skells embedded in tosca-rock — Buenos Ayres to the Colorado — 8. 

 Ventana — BaJiia Blanca ; M. BTermosy, bones and infusoria of; P. 

 Alta, shells, bones and infusoria of ; co-existence of the recent shells 

 and extinct mammifers — Buenos Ayres to St. Fe — Skeletons of 

 Mastodon — Infusoria — Inferior marine tertiary strata, their age 

 — Horse's tooth. Banda Obiental — Superficial Pampean forma- 

 tion — Inferior tertiary strata, variation of, connected with volcanic 

 Cbction ; Macrauchenia Patachonica at S. Julian in Patagonia, age 

 of, subsequent to living mollusca and to the erratic block period. 

 Summaey — Area of Pampean formation — Theories of origin — 

 Source of sediment — Estuary origin — Contemporaneous with exist' 

 ing mollusca — Relations to underlying tertiary strata — Ancient 

 deposit of estuary origin — Elevation and successive deposition of 

 the Pampean formation — Number and state of the remains of 

 mammifers ; their habitation, food, extinction, and range — Con- 

 clusion — localities in Pampas at which mammiferous remains 

 have been found. 



The Pampean formation is highly interesting from its 

 vast extent, its disputed origin, and from the number 

 of extinct gigantic mammifers embedded in it. It has 

 upon the whole a very uniform character : consisting of 

 a more or less dull reddish, slightly indurated, argil- 

 laceous earth or mud, often, but not always, including 

 in horizontal lines concretions of marl, and frequently 

 passing into a compact marly rock. The mud, wher- 

 ever I examined it, even close to the concretions, did 

 not contain any carbonate of lime. The concretions are 

 generally nodular, sometimes rough externally, some- 



