FORT U]S'ION OF CRAZY MOUNTAIX FIELD, MOXT. 31 



THE GIDLEY AND SILBERLING QUARRIES 



The greater part of the National Museum collection, about four- 

 fifths of the identifiable specimens, is from the Gidley and Silberling 

 Quarries, of which the Gidley Quarry is far the more important, with 

 nearly seven times as many specimens as the Silberling Quarry. 



The Silberling Quarry, Loc. 1, was located, as a surface prospect, 

 by Mr. Silberling in 1902, and he subsequently made a small collection 

 here that formed the basis of Douglass' publication in 1908. In 1908 

 Silberling opened the quarry for the National Museum and then 

 collected most of the specimens kno^v^l from this locality. In 1909 

 the much richer and more easily worked Gidley Quarry drew his 

 attention away from the Silberling Quarry, and httle work has since 

 been done there. Silberling has done some farther prospecting, 

 however, and in 1935 the Third Scarritt Expedition reopened the 

 quarry and worked it for a few days, but abandoned it on finding the 

 bed bone poor, the stripping very difficult, the fauna essentially 

 duplicating that of the Gidley Quarry, and the matrix unsatisfactory 

 from the point of view of preparation. This quarry did, however, 

 produce the splendid Ptilodus skull and partial skeleton described 

 by Gidley, and it is the only locality in this field where Psittacotherium 

 or Elpidophorus minor have been found. All its other genera and 

 species are represented by about equally good or better material 

 from other localities. 



The Silberling Quarry is in NE'^SWK sec. 4, T. 5 N., R. 16 E., 

 in an embayment near the middle of the east side of Bear Butte 

 (see pi. 5). The fossil horizon is about 75 feet below the base of the 

 No. 3 sandstone and is the highest level in the No. 2 that has yielded 

 identifiable mammals. The bone layer is not well defined by any 

 visible criteria but is limited to a zone 1 or 1}^ feet in thickness. 

 The matrix is a fine greenish tuft" or shale, very tough and harsh, 

 extremely abrasive to handle, and difficult to work in preparation. 

 It grades laterally into a bed with numerous fresh-water bivalves, 

 among which mammals also occur, but this matrix is so hard that 

 preparation of fragile specimens would be almost impossible. 



The Gidley Quarry, Loc. 4, is in NW}4'NE}^ sec. 25, T. 5 N., 

 R. 15 E. (see pi. 4). It is immediately adjacent to the county road, 

 on its east side, where it descends the steep hill from the basal No. 3 

 rimrock to the valley of the upper part of Widdecombe Creek, on 

 the relativel.y unresistant and topographically negative No. 2 beds. 

 A small coulee here descends the slope, in a westerly direction, and 

 cuts the bone bed apparently near the middle of the rich pocket in 

 which the Gidley Quarry is developed. The locality was discovered 

 by Mr. Silberling as a surface prospect in tliis coulee in 1905. When 

 Dr. Gidley visited the field in 1909, Mr. Silberling showed liim this 

 locality as the most promising of any in the field. The surface 



