ANT-HILL FOSSILS 



2 37 



features of the formation. Our camp lay near the only available water- 

 hole, in an otherwise dry canyon, tributary to Buck creek, which forms 

 the eastern boundary of the area. From Buck creek the land rises 

 gradually to the summit of the divide, whence it falls away to the level 

 of Lance creek on the west. On the eastern slope the strata, which dip 

 toward the west at an angle of about ten degrees, form a succession of 

 outcrops one above the other as one ascends the hill, so that they may be 

 read in orderly sequence beginning with the oldest in the point of time. 

 Beyond the divide the clip of the strata and the slope of the ground 

 coincide so that the revealing outcrops are absent. To the east of Buck 

 creek, on the other hand, on either side of the little canyon wherein our 



Fig. 1. Looking down Speing Ckeek Can vex toward the Ceiutops Beds. In 

 the foreground and middle distance the strata are of marine origin — Pierre and Fox 

 Hills formation — the fresh-water Lance sediments lying beyond. 



cam]) was pitched, the rocks, while still late Cretaceous, are older than 

 the Lance formation and of marine origin, for in them the shells of 

 ancient sea-creatures are abundant. 



Geologists tell us that during Cretaceous time the continent of North 

 America was covered in part by an inland sea having its outlet to the 

 north into the Arctic Ocean and on the south into what is now the 

 Gulf of Mexico. Along the western shores of this Cretaceous sea were 

 long stretches of low-lying lands gradually rising toward the west to the 

 region of the Bocky Mountains, then in their nascent state. The shore 

 lands, which rarely extended much above the level of the sea, were 



