10 F. Ameghino — Geology of Argentina. 



Eepublic^ publislied in 1891, I arrived at the conclusion that there 

 must have existed a genetic connection between the Typotheriidte 

 and the monkeys, and that the original stem of the Primates must 

 be sought for in the deposits of the latest periods of the Cretaceous 

 epoch. The discoveries recently made in the Pyrotlierimn Formation 

 prove that that is actually the case. The Primates of this period 

 completely connect the Homunculidse with the Pi'otypotheriidae, and 

 at present it seems as if the Homunculidse, Protypotheriidae, and 

 Lemuridaj were three divergent branches of one and the same stem. 



The Typotheriidse, finally raised by Zittel to the rank of a sub- 

 order (Typotheria), constitute one of the most singular groups of 

 mammals ; regarded successively first as ungulates, then as un- 

 guiculates, most authors have united them with the Toxodonts, while 

 others have associated them with the rodents and some with tlie 

 edentates. These curious animals, of which the better-known 

 genera are Typotherium, Pachyrucos, Protypotherium, Hegetotherhim, 

 Icochilas, Trachytheras, etc., become then a branch diverging from 

 the same stem whence the monkeys arise, a branch which becomes 

 isolated by evolution since the Cretaceous epoch, and the last repre- 

 sentatives of which (Typotherium) approximate to the Toxodonts 

 through parallel evolution, in the same way that the Proterotheriidas 

 resemble the horses in the structure of their feet without any very 

 close relationship existing between these two groups.^ 



What is the precise geological epoch to which date back the 

 deposits containing the remains of this singular fauna? In my 

 opinion, as I have indicated above, they are decidedly Cretaceous. 



1 rely on the fact that these beds with remains of Pyrothenum 

 everywhere accompany the red sandstones with remains of Dinosaurs, 

 so that it has not liitherto 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 smaller reptiles of types not yet determined;^ while at other 

 points all these remains are shown mixed together, at least to all 

 appeai'ance, always accompanied by a gi-eat quantity of silicified 

 wood. In all parts where it has been possible to examine sections, 

 the Cretaceous beds display a concordant stratification from the 

 bottom to the top, without interruption of any kind, so that it is 

 indubitable that the strata with Pyrotherium have been continued 

 without interruption into those with Dinosauria. Still more ; in some 

 places in the territory of Chubut the variegated sandstones [areniscas 

 abigarradas) of the interior extend even as far as the coast of the 

 Atlantic, and are covered in concordant stratification by the same 

 strata with Pyrotherium, which are submerged beneath the waters of 



^ F. Ameghino, " Los Monosfosiles cle la Republica Argentina " : Eevista Argent. 

 Hist. Nat., vol. i, 1891, pp. 383-97, figs. 86-97. 



2 So much interest has been aroused in the fossils of the Patagonian region that 

 the North American Government has despatched an expedition with the object of 

 collecting fossils for the museums of the United States. This expedition is in charge 

 of Messrs. J. B. Hatcher and 0. A. Peterson, who are already in Patagonia. 



[^ See supplementary note by the translator, p. 21.] 



