MATTHJJW, CLIMATE AND EVOLUTION 193 



of evolutionary change is constant in all parts of the earth, at least for 

 members of the same grtmp. But if the rate varies in different regions 

 for the fauna as a whole, we have no reason to believe that it woukl be 

 constant for common or similar groups. 



The practical application of this method is very unsatisfactory. In 

 illustration of this, I may instance the widely divergent views entertained 

 by different authorities as to the age of the later geological formations of 

 Argentina in comparison with European standards. Able and authori- 

 tative discussions of this problem have appeared within the last few years 

 by Ameghino," Eoth,i^ Gaudry,=^o Scott,-^ Hatcher,^^ Ortmann,^^ Stan- 

 ton, von Ihering, Wilckens, Cossmann, Wiman and otliers, dealing with 

 the vertebrate and invertebrate fossils and stratigraphic relations of the 

 formations. The field work has been extensive, the collections large, the 

 faimre are large and varied and in large part well kno^vn ; but the results 

 are widely discordant. The amount of discordance is indicated by the 

 correlation of the four principal terrestrial formations, as given by 

 Ameghino, Roth, Gaudry and Schlosser. 



The correlation of widely distant formations is so intimately l)ound up 

 with problems of geographic distribution and migration that the two 

 series of problems must be studied and solved together. The methods 

 relied upon by Roth and Ameghino are substantially the same as those 

 generally used by northern authors. Why then do they lead to such dis- 

 cordant results? It is because the data on which they rest prove not con- 

 temporaneity but homotaxis. Granting that two faunae in widely remote 

 regions contain the same proportion of extinct species, granting that 

 they represent equivalent stages of evolutionary progress, they are not 

 thereby shown to be contemporaneous, unless they are at the same dis- 

 tance (measured not in miles but in difficulty of advance) from the main 

 center of dispersal of the fauna which they contain. Very obviously, if 



18 Fl. Ameghino: "L'Age ties Formations Sedimentaires de ratagonie," Anal. Soc. 

 Cient. Argent., torn. L. LIV ; pp. 1-231 of separata. 1903. "Formations Sedimentaires, 

 du Cretace Superieur et dn Tertiaire de Patagonie," Anal. Mus. Xac. Buenos Aires, torn. 

 XV, pp. 1-568. 1907. 



19 Santiago Roth : "Beitrag zur Gliederung der Sedimentablageningen in I'atagonien 

 nnd der Pampasregion." Neue.s .Tahrb., Beil.-Bd. xxvi. s. 92-150, taf. xi-svii. 1908. 



™ A. Gaudry : "Fossiles de Patagonie, etc." Ann. de Pal^ont. I. 1906. 



-1 W. B. Scott : Mammalia of the Santa Cruz Beds in Rep. Princ. Univ. Exp. Pata- 

 gonia, vol. V. 1903. Int. Cong. Zool., Berne, C.-R.. pp. 241-247. 1905. .\ History of 

 the Land ^Mammals of the Western Hemisphere. 1913. 



22 J. B. H.\TCHER : "On the Geology of Southern Patagonia." .\mer. .lour. Sci., vol. iv,. 

 pp. 327-354. 1897. "Sedimentary Rocks of Southern Patagonia." ibid., vol. ix, pp. 

 89-108. Ibid, vol. XV. pp. 483-486. 1903. 



23 A. Ortmanx : Tertiary Invertel)rates in Report Princ. Univ. Exp. Patagonia, vol. iv, 

 pp. 45-332, pll. xi-xxxix. 1902. 



See for further references the bibliography in Ameghino, 1907, supra, pp. 3-18. 



