FOSSIL LAND MAMMALS AXD WESTERN NEARCTIC FAUNA 109 



vided an objective basis for the evaluation of the numbers of in- 

 dividuals of each species in the sample and from this census inferred 

 the species whose ranges were more proximal or more distal to the 

 accumulation site. No doubt other interpretations of the data will 

 differ from Shotwell's, for, as Shotwell notes, many variables and 

 assumptions are involved, but a new method of inquiry has been 

 pioneered. And this approach to the significance of relative num- 

 bers of fossil remains at a given locality will make the formerly 

 indifferent collector think twice before destroying or leaving behind 

 the identifiable fragments. 



The taxonomic composition of quarry samples may differ sig- 

 nificantly from samples made up of specimens picked up only on 

 the surface of a fossil-bearing stratum. Simpson (1937) noted the 

 differences between two such samples in the Paleocene of Montana 

 and concluded that the apparent differences probably represented 

 two facies of the fauna. In a footnote (p. 52) he remarked: "Correla- 

 tions of faunal types and collecting methods are real but indirect. 

 Flood-plain deposition and facies would not normally result in 

 concentration of fossils sufficient to permit profitable quarrying." 

 Van Houten (1945) concluded that in the continental sediments of 

 late Paleocene and early Eocene ages in the Rocky Mountain region 

 there is a definite relationship between mamalian faunal facies 

 and the lithofacies. He found (p. 444) that the arboreal forest 

 faunal facies [micro-mammals] are concentrated in local pockets of 

 the drab grayish sediments, whereas the large ungulates and 

 creodont carnivores, representing savanna floodplain habitats, are 

 sparsely scattered throughout the red-banded varicolored sediments. 

 Here the micro-mammal facies were obtained from quarries and the 

 mega-mammal facies from surface collecting. A comparison of a 

 quarry sample with the surface discoveries from one formation 

 shows taxonomic and census differences comparable to those in the 

 lithofacies studied by Simpson and by Van Houten. Simpson (1935, 

 p. 4) showed the abundance of different species in the Tiffany fauna, 

 late Paleocene, from the San Jose formation of southwestern Colo- 

 rado. In his chart, here slightly modified (Fig. 4) following later 

 work by Simpson, the numbers of micro-mammals from the Mason 

 Pocket faunule, contained in less than a cubic yard of matrix, are 

 compared with the known surface discoveries on the upper Paleocene 

 part of the San Jose formation. In this comparison only one species. 



