J. B. Hatcher — Geology' of Southern Patagonia. 333 



remains from two or more distinct horizons by recent erosion ; 

 which latter has been the cause of much confusion in other 

 instances, as for example, the Loup Fork and Equus beds of 

 our western plains. 



Dr. Ameghino,* in giving his reasons for referring the Pj^ro- 

 therium beds to the Cretaceous, says : " I rely on the fact that 

 these beds with remains of Pyrotherium everywhere accom- 

 pany the red sandstones with remains of Dinosaurs, so that it 

 has not hitherto been possible to separate them in an absolute 

 manner. These sandstones in certain places exhibit nothing 

 but bones of Dinosaurs ; in others they show only remains of 

 mammals and small reptiles of types not yet determined, while 

 at other points all these remains are shown mixed together, at 

 least to all appearance (italics mine), always accompanied by a 

 great quantity of silicitied wood." Now according to Ame- 

 ghino's own statements, in the localities where this Pyrotherium 

 fauna has been found most abundantly, the nature of the 

 country is just such as to bring about a mingling of remains 

 really belonging to quite different horizons, and thus their 

 association in the same horizon may be only apparent, as he 

 himself has in reality suggested. In another publicationf he 

 says : "Malheureusement ce nouveau gisement se trouvait dans 

 une region absolument inconnue et accidentee d'une maniere 

 epouvantable ; il s'egara au milieu de ce labyrinthe et ne put 

 en sortir qu'a dure peine en abandonant une partie du materiel 

 de voyage." I may also add that in the region of Mayer basin 

 and the upper Rio Chalia, especially the former, there have 

 been great disturbances, so that the Guaranitic beds and the 

 superimposed Tertiary deposits are inclined at high angles. 

 In such a region the exact stratigraphic relations of the differ- 

 ent beds are not always easily determined, and in some cases 

 grave errors have arisen through false determinations made by 

 most capable men. As an example of this, it need only be 

 remembered that Senor Carlos Ameghino spent five years in 

 Patagonia, working mostly in the Santa Cruz beds, before dis- 

 covering that they overlie the Patagonian beds,;); all the while 

 considering them as below the latter series (although Darwin 

 had fifty years before suggested the true conditions), § and this 

 far out from the mountains and in a region singularly free 

 from faults or dislocations of any kind, where the strata are 

 approximately horizontal and succeed one another in regular 

 order. 



* Loc. cit. 



f See Premiere Contribution a la Cormaissance de la Faune Mammalogique des 

 Couches a Pyrotherium. Florentino Ameghiuo, Bol. del Inst. G-eo. Arg., tome 

 xv, cahiers 11 et 12. 



\ See Enumeration Synoptique des Especes de Mammiferes Fossiles des Forma- 

 tions Eocenes de Patagonie, par Florentino Ameghino. Buenos Aires 1894, pp. 

 1-8. § See Geol. Observ. on South America, p. lit. 



