520 FLORA OF THE LAKAMIP: GROl'P. 



tamineje may have declined somewhat, as have more probably the 

 Aroidere. It is at least evident that in considering the monocotyledo- 

 noiis orders wc are confronted by a set of conditions tlie reverse of those 

 we mot with in the ferns and the Oonifer;B, viz : all our formations are 

 now below the period of maximum development of the group under 

 consideration, and the opposite results must be expected. These, in 

 fact, we find. The palms furnish 00 species, which, evenly distributed, 

 would give the Senoniau 14, the Laramie 13, and the Eocene 33 ; but 

 the Senoniau gets only 4, while the Laramie gets 17, the Eocene afford- 

 ing the remaining 39. lu this important order, therefore, the Laramie 

 is about as fully represented as the Eocene, a fact which has been used 

 to its full extent in arguing for the Eocene age of the Laramie group. 

 If, however, we take the other niouocotyledonous orders together, we 

 finfl that the Laramie (14) falls considerably more below its quota (21) 

 than the Senoniau (10) falls below its quota (23), which might equally 

 be taken to argue its (Jretaceous age. 



In discussing the numerous dicotyledonous orders, we can only select 

 those whicli are most important, either from their abundance in the fos- 

 sil state or from certain peculiarities or anomalies which they present. 

 As all trace of the earliest beginnings of this great subclass is still with- 

 held from human observation, it is difficult to describe the rise and de- 

 cline of its several subdivisions, but it seems probable that the mono- 

 chlamydeous forms were not only the earliest to appear, but that at the 

 period when we tirst make their acquaintance (the middle Cretaceous) 

 they had nearly attained their acme of growth and diversitj'. We then 

 find the large families Salicine;e, Oupuliferai, Urticacea', and Laurinese 

 in great profusion and highly developed, while many forms which are 

 now dichlamj'deous, though they might not then have been so, had 

 already come upon the scene. In examining some of these large orders, 

 the principal question we have to ask is. Does their occurrence in 

 the Laramie group more nearly resemble that in the Eocene or in the 

 Senoniau, or rather, assuming that the divergence of the Senoniau and 

 Eocene; as known quantities, indicates difference of age, does the diverg- 

 ence of the Laramie from the Eocene indicate for that group an age at 

 all earlier than the latter? The comparison, as in former cases, must 

 be with even quotas and not with the actual figures. The SalicineiB 

 furnish 50 species to the three formations. The quota of the Eocene 

 would be 31, and we find 10 ; that of the Senonian should be 13, and we 

 find 14. An intermediate i^osition would make the Laramie fall some- 

 what short of its quota (12). As a matter of fact it more than doubles 

 it (20). So far as this order would indicate, therefore, the Laramie 

 would be decidedly subSenonian. This is due to the great predomi- 

 nance of the genus Populus in the Laramie group, of which more will 

 be said hereafter. 



The Cupuliferaj furnish 140 species. Of these the Eocene has 58, 



