FORT UXION OF CRAZY MOUNTAIN FIELD, MOXT. 29 



area, to the western part of T. 5 N., R. 14 E. Here the wide pass 

 between Porcupine Butte and Cayuse Butte is in the very broad, 

 poorly marked syncline or basin. The beds around Porcupine Butte 

 dip northeasterly into this area, although in the Butte itself the dip 

 (about 5°) is nearly north. 



There are a few visible small faults with a throw of a few feet, such 

 as one at the Silberlmg Quarry, but these are negligible in beds of 

 such great thicloiess. No faults of sufficient importance to show on 

 the map or to affect stratigraphic leveling significantly were detected. 



The deformation appears to have been entirely post-Fort Union, 

 and nowhere in this region was any angular discordance detected 

 between the various Cretaceous and Tertiary formations, even down 

 into the Lower Cretaceous (Kootenai) in the domes north of this 

 area. It is a reasonable assumption that the deformation was approx- 

 imately contemporaneous with the post-Paleocene igneous intrusions. 



FOSSIL LOCALITIES AND FAUNAL LISTS 



GENERAL OCCURRENCE OF FOSSIL MAMMALS 



Fossil mammals, represented at least by material adequate to show 

 its mammalian nature, have so far been found at 57 locahties in this 

 field, of which about 35 have yielded material sufficiently well pre- 

 served for generic identification, and about 25 material specifically 

 identifiable and of some real value in correlation and faunal studies. 

 The great bulk of the collections comes, however, from the three locali- 

 ties where quarries have been developed. 



Although some of the more resistant sandstones, such as those in 

 the No. 1 beds or the basal sandstone of the No. 3 beds, are well ex- 

 posed and form more or less continuous outcrops wherever they occur 

 in the field, the finer and less resistant sandstones and the shales and 

 clays are on the whole very poorly exposed. Bones are occasionally 

 found in the sandstones, but they are there very rare and are generally 

 of no value. Only one identifiable mammal has ever been found in a 

 true sandstone in this field. The mammal locahties are therefore 

 almost entirely on the rarer shale exposures, which occur where coulees 

 have cut the shale slopes or where the wind has developed blow-outs. 

 Such exposures, seldom as much as a hundred yards in diameter and 

 generally much less, are limited in number. In the productive area in 

 this field there are probably not over 400 of them, and all of these have 

 been prospected by Mr. Silberhng, manj^ of them also by me or others. 



The mammal occurrences may be grouped under two categories, as 

 surface localities or as (actual or potential) quarries. At the surface 

 localities, much the more numerous of the two, the mammal remains 

 are rare, as far as loiown, and are so sparsely scattered through the 

 matrix that only accidental finds or concentration from long weather- 

 ing and wind erosion leads to any production. The ideal conditions 



