30 BULLETIN 169, UNITED STATES NATIONAL MUSEUM 



at such localities are deep weathering in situ without erosion or surface 

 drift or wash, combined with gentle deflation, which removes the 

 small weathered shale particles but leaves the larger or heavier fossils. 

 Such conditions are relatively rare, and it is also noteworthy that 

 numerous localities that were in good collecting condition when first 

 found 30 years or so ago have now lost much of their value or promise 

 by drifting over of windblown material or surface wash, by the spread 

 of vegetation onto their weathered surfaces, or by active erosion, 

 which removes the surface concentrates and leaves only a clean, hard 

 shale exposure in which there is little chance of finding a fossil in situ. 



The quarry localities are those where fossils are so concentrated in a 

 local pocket that it is profitable to work the bed as a whole and recover 

 fossils in place. The difference is, of course, of degree and not of 

 kind but is one of great practical importance. Were it not for its 

 three principal quarries, which have been called the Gidley, Silberling, 

 and Scarritt Quarries, this field would be of relatively little importance. 

 There are marginal locahties also of some importance, intermediate 

 between quarries and straight surface localities. Thus Loc. 81 (as 

 listed below) was hterally a quarry, but the whole bone pocket and 

 therefore quarry was only about a yard in diameter. Loc. 25 has 

 yielded so much surface material that a concentration of probable 

 quarry calibre is indicated, but the rather limited attempts made 

 to quarry at that locality have not in fact developed a profitable 

 bone layer. 



An outstanding characteristic of the field, regardless of level or 

 geographic position, is the fragmentary nature of the material. In 

 the hundreds of specimens collected, there are so far Imown only four 

 or five mammal specimens complete enough to be called skulls, and 

 only two of these really adequately reveal most of the skull structure. 

 Only about 10 specimens include associated upper and lower teeth, 

 and only three any surely associated limb bones. Nothing approach- 

 ing a complete skeleton has ever been found. This fragmentary con- 

 dition is seen not only in the surface specimens but equally in those 

 found in situ deep in the quarries. The quarry specimens commonly 

 show fresh breaks that look recent and yet abut against undisturbed 

 matrix. It is also peculiar that most of the quarry specimens had 

 lost some of their teeth before burial and that jaws quite devoid of 

 teeth are relatively abundant. 



For his own records and in connection with the National Museum 

 collecting, Mr. SilberUng has numbered every locality where any fossils 

 were found. These serial numbers are here adopted and are those used 

 throughout the present work. There are now 82 numbered localities; 

 25 of these are not mammal localities, but for completeness and the 

 convenience of later workers they are all given in the serial list on a 

 later page. The map (pi. 1), however, shows only mammal localities. 



