wAiu..] DISCUSSION OF THE TABLE. 519 



total of the two floras. The Laramie flora is 21 per cent, of the three 

 combined floras, the Senonian is 23 per cent., aud the Eocene 56 per cent. 

 The quota of each, therefore, were they all of the same age, would be : 

 Laramie, 32; Senonian, 36; Eocene, 87. It will be seen that the Seno- 

 nian far exceeds its jiroportion, even assuming for it a considerably 

 lower position. We are thus forced to see in the Senonian flora a much 

 stronger Mesozoic facies than in either of the other groups. No family 

 of plants brings out this fact more clearly than that of the Ferns, but it 

 also speaks with equal authority upon the position of the Laramie below 

 the recognized Eocene plant beds as thus far known. 



The Ehizocarpene, Equisetacete, and Lycopodiaceie can best be men- 

 tioned when we come to consider the genera, and we will now pass to 

 the two gymnospermous orders, the Cycadace* and the Coniferae. The 

 Gycadaceie, although they have barely survived into modern time, are, 

 as is well known, a characteristic Mesozoic tj'pe of vegetation, having 

 attained their maximum development in the Jurassic. They form an 

 insigniflcaut part of the Cretaceous flora and nearly disappear with 

 the Tertiary. The only Laramie species rests upon a single specimen 

 found at Golden, Colorado, and referred by Mr. Lesquereux to the 

 genus Zamiostrobus. Yet seven species belonging to almost as many 

 genera are recorded from the Senonian, again remindijig us of the Meso- 

 zoic age of this flora. 



We are thus brought to the consideration of the Coniferae, which is 

 one of the most important orders in the vegetable kingdom for the pa- 

 leontologist. In the three formations under consideration this order has 

 thus far yielded 107 species, of which 17 are found in the Laramie, 36 in 

 the Senonian, aud 58 in the Eocene, there being four coincidences. 

 The even quota of each would be: Laramie, 23; Senonian, 26; and 

 Eocene, 62. As the Coniferae probably attained their maximum devel- 

 opment in the middle Cretaceous, that is, earlier than any of the three 

 epochs we are considering, the older of these epochs should show an 

 excess over this quota and the younger a deficit. The Senonian shows 

 such an excess and the Eocene such a deficit, but the Laramie also falls 

 below even farther than the Eocene, which, in so far as the evidence of 

 this order goes, gives it a more modern aspect than the Eocene. 



Passing to the monocotyledouous orders, we find them, with the ex- 

 ception of the Palm Family, too small to afford any reliable criterion 

 for the settlement of questions of age. The Naiadaceae and Gramineae 

 are the only other orders at all approaching the ijalms, and both these 

 display decidedly modern characteristics, compared with any of the types 

 hitherto considered. If the palms reached their highest state and great- 

 est abundance in Eocene time, the grasses did not probably attain this 

 position before the close of the Miocene, and it may be doubted whether 

 they have attained it at the present time. The same may be said for 

 the Cyperaceae and perhaps for the Naiadaceae. The Liliaceae and Sci- 



