wAUu.j DISCUSSION OP THE TABLE. 521 



a number about one-third below its quota (82), while the Senonian has 

 52, a number as mu<;li above. The Laramie occupies a strictly inter- 

 mediate position, yielding 36 species, or live more than its quota. In the 

 Urticaceie the Laramie deviates more from the Eocene than does the 

 Senonian and in the same direction as in the Salicineic, while in the 

 LaurineiB the deviation is again intermediate. In the Juglande;e we 

 again have the Laramie showing an exaggerated Mesozoic tendency. 



We thus see that none of the apetalons orders give the Laramie the 

 same position, from this numerical point of view, as the Eocene, all 

 placing it lower and either intermediate between the Eocene and the 

 Senonian or below the latter. 



The principal polypetalous orders are the Araliacese, the Myrtacese, 

 the Eosaceae, the Anacardiacete, the Sapiudacese, the Bhamneae, t|je 

 CelastrineJE, the StercuHaceie, and the Magnoliace:ie. They are much 

 more decidedly Eocene in aspect than the apetalous orders, but less so 

 than they appear with the proportionally large figures in that column. 

 In fact, the Eocene generally only slightly exceeds its quota for the three 

 groups after equalization as explained above, and in the Rhamneje and 

 Magnoliaceae it falls below it. A careful inspection of these nine orders 

 shows that in two cases (the Kosaceae and the Sterculiacete) the Laramie 

 holds an intermediate place between the Eocene and the Senonian, that 

 in four cases it holds a place below the Senonian, while in three cases 

 (the Anacardiaceae, Sapindace:ie, and Magnoliacew) its position is indi- 

 cated as slightly higher than the Eocene. 



The gamopetalous orders are small and their indications are readily 

 deduced from a casual inspection of the table. The two largest, the 

 Ebenacese and (Japrifoliacese, consist entirely of the two genera, Diospy- 

 ros and Viburnum, respectively, and can be treated under the head of 

 (jenera. Taking all the gamopetalous orders together, the Laramie is 

 seen to occupy an intermediate position between the Senonian and the 

 Eocene. 



In examining the orders represented in the three formations under 

 consideration, especially the smaller orders, a marked tendency is visi- 

 ble toward the confinement of entire ones to one formation. This is 

 due to geograi)hical peculiarities, a characteristic which, when we come 

 to study the genera, can be no longer ignored. 



We are now prepared to consider our subject from the point of view 

 of the genera, and before going further it will be necessary to point 

 out some of the difficulties of this method. In vertebrate paleontology 

 the genera are nearly all extinct, and therefore the paleontologist 

 may here legitimately employ his genera as reliable data for the 

 determination of the age of the formations to which they are confined. 

 In vegetable paleontology this is by no means the case. Of the 354: 

 genera represented in the three formations only 165 are extinct, and 



