100 CONTRIBUTIONS TO PAL^ONTOLOGY 



As regards frequency of occurrence, the foUowing 13 species are recorded from 

 f our or more of the type Lance localities : 



Dryophyllum subfalcatum 6 Viburnum marginatum 5 



Querous? viburnifolia 6 Dombeyopsis trivialis 4 



Salix lancensis 6 Equisetum sp 4 



Typha sp 6 Platanophyllum montanum 4 



Fraxinus lcii 5 Vitis stantoni 4 



Sequoia dakotensis 5 Grewiopsis saportana 4 



Trapa? microphylla 5 



A comparison of this Hst with that of the 10 species which are of greatest indi- 

 vidual abundance shows that 7 of the latter are also among the 13 most persistent 

 species of the Lance flora, as at present known. The remaining 3 species are very 

 abundant locally but are each restricted to two of the nine Lance Creek locaUties. 



CLIMATIC CONDITIONS INDICATED BY THE LANCE FLORA 



There are in my opinion two reUable methods of employing fossil plants as 

 indicators of cHmatic conditions of the past; both methods apply only to floras of 

 late Mesozoic or Cenozoic time, and each method is wholly independent of the 

 other. These are (1) an analysis of the structural characters of the dicotjdedonous 

 leaves (chiefly size, venation, texture, and marginal characters) as compared with 

 modern leavcs of known chmatic rcquirements; and (2) a generic and specific com- 

 parison of fossil species with hving forms whose climatic requirements are known, 

 on the assumption that the past conditions wcre analogous to those under which 

 the majority of the closcly related Uving species grow. 



The apphcation of these methods to carly and middlc Tertiary floras has been 

 described by Chaney and Sanborn,' MacGinitie,- and Potbury.^ The details of 

 their appHcation to Upper Cretaceous floras are contained in my report on the 

 Medicine Bow flora.^ Ahhough neither of these methods is strictly quantitative, 

 they are considered much more accurate than conchisions based on individual 

 species or genera, particularly since each method may be used as a check against 

 the other. 



The analyses of the leaf characters of the dicotyledonous Lance spccies are 

 shown in table 1. For purposes of comparison the table also includcs analyses of 

 various modcrn and fossil asscmblagcs studicd by tlic authors mentioncd above or 

 by me. In each catcgory in the table the Lance flora stands between the warm 

 temperate to subtropical floras and the subtropical to tropical. The perccntage of 

 entire-leaved species in the Lance flora (54 per cent) is similar to the highest figure 

 obtained by Bailcy and Sinnott for warm temperatc forests.^ This is in agrcement 

 with thc intermediate position of this flora, in rcsj^cct to this character, bctween the 

 warm temperate WeaverviHe flora and the subtrojncal Goshen flora. In their com- 

 parative lengths the Lance species are between the warm temperate La Porte flora 



' Chaney, R. W., and Sanborn, E. I., Carncgic Inst. Waah. Pub. No. 439. 18, 1933. 

 ' MacGinitic. H. D., CarncRio Inst. Wash. Pub. No. 405, 11.5. 1937. 



• Potbury, S. S., Carncgio Inst. Wa«h. Pub. No. 465, 52, 1935. 



* Dorf, E., Carncgio Inst. Wash. Pub. No. 508, pt. I, 25-31, 1938. 

 •Bailey, E. W., and Sinnott, I. W., Science, n. s.. vol. 41. 832, 1015. 



