FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 21 



times included in "Wasatch", sometimes in Fort Union, and sometimes 

 are separated from both as an intervening stage. 



As a matter of personal opinion, I would prefer to use "Fort Union 

 group" for the whole Paleocene series of this northwestern plains- 

 area, to include all strata of age equivalent to or intermediate between 

 the Puerco and the Clark Fork. This usage is very broad, but the 

 designation "Fort Union" has already been so loosely applied that a 

 more restricted usage would be very difficult to frame or to maintain. 

 It at least has the virtue of being on the whole a natural subdivision 

 of the Tertiary and of including practically all the beds that have 

 ever been called Fort Union, except in out-and-out error or in such 

 wholly untenable classifications as that of Knowlton. For more 

 precise work it will in any case be necessary to defi.ne and use more 

 local names for particular formations and members included in the 

 Fort Union group. 



In this field, the earliest workers recognized as Fort Union only 

 the beds from the basal No. 3 sandstone (as defined on a later page) 

 upward. Douglass, Stone and Calvert, Stanton, and all later workers, 

 however, have also included the underlying andesitic beds called Lebo 

 by Stone and Calvert. The name "Fort Union" is used tliroughout 

 the present study for the Lebo and all higher early Tertiary strata 

 in the area here considered. The uppermost part of this series is of 

 unknown age and may possibly be as young as the Gray Bull, in which 

 case it should be removed from the Fort Union, but at present no 

 evidence warrants this step. In addition there is a series of strata^ 

 the Bear, hitherto always considered as Cretaceous and referred to 

 the Lance, but in my opinion possibly Tertiary. If it should prove 

 to be Tertiary, I would place it in the Fort Union, but tliis is now 

 doubtful, and in this study the word "Fort Union" is not intended ta 

 include the Bear. 



The local Fort Union, thus defined, includes three mappable litho- 

 logic units of very unequal tliickness. Mr. Silberling, who first recog- 

 nized these units, has applied numbers to them, with Fort Union 

 No. 1 at the base and No. 3 at the top, and his field designations have 

 been employed in pubUcations by Stanton, Osborn, Gidley, and others. 

 In accordance with the general rides of stratigraphic nomenclature, 

 local geographic names are here applied, but throughout this discus- 

 sion I shall also employ Silberling's numerical designations. The 

 correspondence is as follows: 



(No. 3 = Melville (new name) . 

 No. 2] 

 No. ij ^ °' 



The No. 1 and No. 2 beds are generally similar, and both are 

 included in the Lebo of Stone and Calvert, but they are easily sepa- 



