STRATIGRAPHIC POSITION OF LANCE FORMATION 365 



the erosion interval represented is of considerable magnitude, or 

 else that the formation is peculiarly variable in thickness. 



"In general the zone along the contact between the Fox Hills 

 sandstone and the Lance formation is poorly exposed in this region, 

 but in the majority of localities where exposures were adequate 

 careful study disclosed evidence that deposition was not continuous 

 from one formation into the other. In a paper 1 on this subject 

 Doctor Stanton admits the occurrence of an unconformity at this 

 horizon in the Dakotas but attaches no particular significance 

 thereto, stating that channeling would normally be expected in 

 the change from marine to land conditions and giving especial 

 weight to the fact that a marine Fox Hills fauna is found com- 

 mingled with brackish-water types above the unconformity. He 

 states that 'The paleontologic evidence consists of distinctive 

 Fox Hills species belonging to such marine genera as Scaphites, 

 Lunatia, and Tancredia, found directly associated in the same 

 bed with the brackish-water forms and occurring with them in 

 such a way that they must have lived together or near each other 

 and been imbedded at the same time.' 



"From the above quotation the inference is plain that Dr. 

 Stanton concludes that the faunal evidence demonstrates with a 

 fair degree of certainty that the unconformity is of minor rather 

 than of major significance. To this conclusion the stratigrapher, 

 is, of course, not qualified to object with authority, but it seems 

 to the writer that the evidence may be looked at from two diver- 

 gent points of view. Because Fox Hills fossils occur in the lignitic 

 shales at the base of the 'somber beds' and mingled with the 

 brackish water types of the Lance formation is not necessarily 

 proof positive that the various faunas lived at the same time ; for if 

 the deposition of the Fox Hills was followed by a definite erosion 

 interval, what is more probable than that in the deposition of suc- 

 ceeding strata fossil shells would be eroded from the marine beds 

 and carried into channels, there to mingle with the then living 

 brackish- water fauna of the Lance formation ? 



1 T. W. Stanton, "Fox Hills Sandstone and Lance Formation ('Ceratops Beds') 

 in South Dakota, North Dakota and Eastern Wyoming," Am. Jour. Sci., XXX 

 (iqio), 178. 



