<ic. Till-: AMF.niCAS MrsijM .loriix.iL 



Sticli rcinlcrs will naturally he iiiij)rcssc<l with the ciioniious lapse of 

 time re(|uire(l for the historical progression outlined in tlii> l)()ok, especially 

 when they consider the \arions <>sTiniates, ran^in<: from three to six millions 

 of years, which ha\<' hecn assigned l)y ditt'erent in\c>tiirators as the time 

 e(ini\alent of the 'I'ertiary period, .\e\ertheless this period co\crs only 

 the later chapter> in manunalian history. Fortheciass of which man is now 

 the dominant memher was already rej)resented hy certain lit t Ic-kiiown 

 forms in the Triassic, at a time when the dinosam's ha<l not yet attainctl 

 their prei'Muincncc and lonu' hefore the Kocky Mountains were uplifted. 



Theflia^ram lici'c I'cproduccd sunnnaii/,c> the lii-toncal snccc»ion of the 

 Tertiary and (Quaternary formations in western North America, jii\in^^ the 

 maximum thickness of each ami distin^nishinti' the deposits of the (ireat 

 Plains from those of the llocky Mountains. The "/ones'" are time peri- 

 ods, named from mammalian f:;enera that are especially characteristic of 

 the corresj)ondin>i formations, while on tlu- extreme riyht ai'c the names 

 of some of the other mammals that sei'\ c as time markers in the " chronom- 

 eter of e\()luti()n." 



This diagram epitomizes a part of the results of Professor Oshorn's 

 studies on the "correlation of Tertiary mammal horizons in Europe, Asia 

 and North .\n)crica,"' a jjrohlcm which has heen slowly worked out with 

 the aid of many colleairues in this counti\\' and abroad. Fi'om these 

 ilata he draws some \-ery far-i'eachini;' conclusions on the origin and 

 spreadinir of f;umas from continent to continent, and on the appearance 

 and remoxal of iicou:raphical harriers to faunal interclianii'c. Such con- 

 clusions in\-est the dry facts of j^eograpliic and jjeoloijic distribution 

 with a larger atid more fruitful meaning;. 



llejjarding the evolution of mammals, the introduction deals \-cry 

 clearly with the rise of paheontoloyy and with the laws of exolution of the 

 teeth, feet and skull. The " irre\ersil)ility of cNohition" and the causes of the 

 extinction of mammalian species are amonu the many topics of i^M-ncral 

 l)i()lof<ical interest. 



\'ery j^'ratifyinjr is the fact that this Museiun has heen able to furnish 

 a \nriiv part of the material for a work of sucli far-reaching importance to 

 the student of manunalian e\()lution. Many of the mounted skeletons 

 in the Hall of k'ossil Mammals appear here, acc<)m])anied hy excellent 

 restorations from the gifted brush of ( harles i{. Knight. The numerous 

 and thorough Museum expeditions in the West and eNewhere, which ha\-e 

 l)een carried on systematically during the past twenty years, furnish scores 

 of field pictiM'es, maps and geological sections. The mam'fold systematic, 

 faunal ami stratigrajjliic studies by Professor Osboiii, Dr. Matthew and 

 others, luive thus been joined synthetically with the results of paheontolo- 

 gists and geoloirists the world o^•cr. 



