_South America._ The two discoveries mentioned in the preceding chapter were made in the so-called Pampas formation of Argentina. This formation has been subdivided by geologists into three successive portions, viz. upper, middle and lower. The distinction is based partly upon evidence derived from the actual characters of deposits which differ according to their level. But the molluscan fauna has also been used as a means of distinction. The whole formation is stated by some to be fluviatile. Other observers speak of it as Löss. This need not necessarily exclude a fluviatile origin, but speaking generally that term now suggests an aerial rather than a subaqueous deposit. The upper subdivision is designated the yellow löss in contrast to the brown löss forming the middle layer. Opinion is much divided as to the exact geological age of the Pampas formation. Ameghino refers it to the Pliocene period, excepting the lower divisions which he regards as upper Miocene. Professor Lehmann-Nitsche assigns Pliocene antiquity to the lowest subdivision only. Dr Steinmann regards the middle and lower subdivisions as equivalents of the 'older' löss of European Pleistocene deposits. The latter determinations are more probably correct than is the first. _Baradero._ The Baradero skeleton was obtained from the middle formation or brown löss, in a locality marked by the presence of mollusca corresponding with modern forms, and contrasted with the Tertiary Argentine mollusca. The skeleton was in a 'natural' (_i.e._ not a contracted) position, the head being depressed on the front of the chest. No associated implements or remains of mammalian skeletons are recorded. _Monte Hermoso._ The vertebra and femur were found in the lower subdivision of the Pampas formation. We have seen that Ameghino refers this to the Miocene epoch: Lehmann-Nitsche speaks of it as Pliocene, Steinmann's opinion suggests a still later date, while Scott also declares that no greater age than that of the Pleistocene period can be assigned. The two specimens were obtained at very different times, an interval of many years separating the dates of the respective discoveries. So far as is known, no mammalian or other animal remains have been yielded by the strata in question, so that the whole case in regard to evidence is one of the most unsatisfactory on record. Indeed the whole question of 'dating' the Argentine discoveries, whether absolutely or relatively, must be regarded as an unsolved problem.