LANCE FLORA OF EASTERN WYOMING 103 



msiy at once be observed from the totals of this table that the floral assemblage is 

 neither strictly cool temperate nor strictly tropical. Without exception, moreover, 

 the cool temperate and tropical distributions belong to genera which are known to 

 thrive — often thrive best — also under warm temperate or subtropical conditions. 

 In contrast, the table shows that 16 of the modern correlatives do not grow under 

 cool temperate conditions and 17 do not grow under tropical conditions, whereas all 

 the species are apparently at home in warm temperate or subtropical regions. The 

 sHghtly higher number of warm temperate correlatives would imply that the Lance 

 assemblage is more nearly warm temperate than subtropical. This conclusion is 

 precisely the conclusion reached on the basis of the leaf characters of the Lance 

 species. In this connection it should be noted that the dominants of the Lance 

 fiora (p. 99) belong to genera which are warm temperate rather than subtropical 

 in modern distribution. 



The above inferences regarding climate are supported by the fact that there 

 are a number of genera or families whose presence togetlier in the Lance flora indi- 

 cates a lowland coastal-plain environment. These include Canna?, Trapa?, Saba- 

 lites, and Pistia, all of whose modern relatives are typically restricted to or best 

 developed in the humid coastal lowlands of subtropical to warm temperate regions. 



In summary it may be stated that the leaf characters and the distribution of 

 modern correlatives of the Lance species, as well as the absence or scarcity of typi- 

 cally cool temperate genera, point to humid lowland conditions of growth under a 

 warm temperate to subtropical climate, more nearly approaching the former. 



CORRELATION 



General principles and niethods — It must, I believe, be admitted that there is no 

 empirical quantitative means of exact correlation between rocks of different regions. 

 Certain fundamentals have, to be sure, graduaUy developed as guiding principles.' 

 But each investigator must carefuUy weigh, qualify, and modify each principle in 

 the light of his own experience to suit the facts and conditions which he encounters. 



In the present analysis, the principles which have been most applicable and 

 useful in the correlation of certain Upper Cretaceous deposits of the Rocky Moun- 

 tain region are as follows: 



1. If two or more fossil assemblages are essentially identical, the rocks from 

 which they were obtained are considered contemporaneous. This principle is not 

 considered infallible. In the first place, it must be remembered that a fossil as- 

 semblage is neither more nor less than a recovered sample of the remains of the 

 living organisms which inhabited the region at the time of fossilization. All samples 

 are not necessarily fair samples; for example, some may be too small. A small 

 assemblage of 20 species which are identical with 20 out of 30 species of a second 

 assemblage is not necessarily contemporaneous with the second assemblage, if the 

 20 species happen to be long-ranging types. In the second place, in view of the 

 element of chance involved both in the preservation of organisms and in the re- 



'Berry, E. W., Maryland Geol. Surv., Lower Cretaceous, 153, 1911. Clark, W. B., U. S. Geol. Surv. BuU. 141, 

 47-53, 1896. Neaverson, E., Stratiffraphical Palsontology, 1-14, 1928. 



