Oeology and Mineralogy. 149 



IS widely the bo^t authorities differ ; partly because European 

 of ovolotricnl au^e avo not always good for use in America, 

 artlv, aKo, from deficient American testimony. We are dis- 



Miocene — as must he true if T.esquerenx's conclusions are rip-lit. 



SecoNdh/. Mammalian fo^vils are a lar safer criterion of geolog- 

 ical age than f()>Nil plants— since the changes in the species of 



greater than in those of plants; and as the mammals of the beds 

 next a!)ove the (^ireen Kiver beds are strongly Eocene in their 

 cliaracteristics— as attested to by I-eidy, Marsh and ('ope — it is 

 exceedint-lv improbable that the beds aifbrding the fossil mammals 

 should he rp])er Miocene, or Miocene at all. 



Thirdhj. if the beds containing these mammalian remains, to- 

 gether ^^irh the nnderhi'iag (rre" 

 the Evanvtoii be<ls, and the Car 



also, /o/z/'^/j^y, that the ".Miocene" features of the plants of the 



hence., /(/-Wy, that the diversities in tJie cotemporaneous Tertiary 



be made of the faets from one continent for fixing the chronology 

 of beds in the other. 

 It is probable, that p 



quereux, to many of the Miocene 



ously existed as Eocene or Cretac 



If the fossil 4)lants an^ an unce.t: 



