120 



C O N T R I B U T I O N S TO P A L ^E O N T O L O G Y 



Paleocene age. Pending the much-needed revision of Rocky Mountain Paleocene 

 floras, at present being undertaken by Dr. Roland W. Brown, of the U. S. Geological 

 Survey, it may be observed that of a total of over 250 Paleocene species there are 

 only 30, of which 15 are very doubtful, which are reported as extending from the 

 Paleocene into the Lance or from the Lance into the Paleocene. These are as 

 follows : 



?Aralia notata 

 Araliffiphyllum artocarpoides 



?Araucarites longifolia 

 Celastrus? taurinensis 

 Cercidiphyllum arcticum 

 Cercidiphyllum ellipticum 

 Dillenites cleburni 

 Diosp3'ros brachysepala 



?Euonymus xantholithensis 



?Ficus coloradcnsis 



?Ficus planicostata 



?Fraxinus leii 

 Ginkgo adiantoides 



?Hicoria antiquora 



?Laurophylkim coloradensis 



Laurus primigenia 



Magnolia magnifolia 

 ?Magnolia pulchra 



Platanus aceroides 



Platanus raynoldsii integrifolia 

 ?Quercus? viburnifolia 



Salix angusta 

 ?Sapindus affinis 

 ?Sequoia dakotensis 



Sequoia nordenskioldi 

 ?Taxodium occidentale 



Thuja interrupta 



Trapa? microphylla 

 ?Viburnum antiquum 

 ?Viburnum whymperi 



This Hst shows an extremely small number of species that are known definitely 

 to bridge the span between Lancian and Paleocene time. They represent only 

 about 6 per cent of the total number of species of either the Lancian or the Paleocene 

 assemblage. It is difficult to explain this great difference between the typically 

 Lancian forests and those of the Paleocene of the same general region, particularly in 

 view of the apparent conformity between the Lancian and Paleocene rocks. I am 

 not prepared to offer an explanation, though I beUeve it may be sought in one or 

 another, or some combination, of the following suggestions: (1) there may exist an 

 unrecognized hiatus between the Lancian and Paleocene deposits; (2) there have as 

 yet not been a sufficient number of specimens coUected from the upper parts of the 

 Lancian formations or the lower parts of the Paleocene to present a true picture of 

 the floral changes; (3) the late Lancian orogeny in the Rocky Mountain region may 

 have been of sufficient intensity to cause rather sudden and widespread environ- 

 mental changes and concurrent floral changes; (4) the sudden floral cliange in the 

 early Paleocene may have been a result of a rather rapid invasion of the Rocky 

 Mountain region, possibly from eastern North America by way of the newly opened 

 route around the north end of the early Paleocene Cannonbafl sca. 



Other floras — There are other floras in the Rocky Mountain region and clse- 

 where which have a few species in common with that of the type Lance formation, 

 as is shown in table 3. These floras are, however, too remotely related to that of 

 the type Lance or other formations of Lancian age to be considered further at the 

 present time. 



Index species and dominanls of Lancian floras — From the foregoing analyses 

 it is evident that there are a number of species in the flora of the type Lance which 

 are, so far as is known, restricted elsewhere to floras of Lancian age. These are 

 shown, along with those of wider stratigraphic rango, in tal)le 4. TheoreticaUy, 



