28 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



East of the high ridge along which the sedimentary section was made, 

 already referred to as Crowfoot Ridge, the strata are folded and faulted in 

 a pronounced, though not an extreme, manner. In the short spur between 

 the two branches of the drainage east of the ridge there is a marked bend 

 in the beds of limestone, which in the higher part of the spur dip steeply 

 and can be traced continuously into the main body of the ridge, but at the 

 lower end of the spur are nearly horizontal. There is thus a short fault 

 line west of the spur, which runs out in the head of the gulch, and probably 

 joins a longer fault which terminates somewhere near the junction of this 

 drainage with the Gallatin River, as shown on the map There is also 

 evidence of horizontal thrust in the telescoping of the limestone layers, 

 which is seen on the east escarpment of the ridge. 



The next spur east of the one called Section Ridge is a long low ridge, 

 formed of nearly horizontal beds, with a slight syncline across its middle, 

 the axis of the syncline being about northwest and southeast. At its south- 

 ern end the beds turn up abruptly against the gneiss ridge, and the shaly 

 horizons are -eroded down, and do not rise in a high spur as erroneously 

 drawn on the general map. There is a fold or bend in the strata as they 

 come from Section Ridge, the beds curving down toward the east so as to 

 permit the strata in the low spur to lie at a low angle. This is probably 

 accompanied by slight faulting, with north-south trend, situated near the 

 bottom of the drainage. It was not observed, however, in the field. 



Between this spur and the next large spur, about a mile east, there is a 

 broad fold in the strata. The beds that dip at a low angle of about 20° to 

 the north and northeast, arch over, to an abrupt pitch with steep angle at the 

 east side, near the south end of the east spur. This general arch is compli- 

 cated by minor folds, not indicated on the map. The changes in dip and 

 the differences in hardness of the shales and limestones show themselves in 

 the topography, which is modified by glaciation. The easier degradation 

 of the shaly layers leads to sink holes beneath stronger limestone layers. 

 One has been made in the lowest micaceous shale, with the first massive 

 limestone layers to the north. Farther east a small rock -bound glacial lake 

 occurs on the gneiss at its contact with basal quartzite. North and north- 

 east of this lake the lowest belt of Cambrian limestone forms a bench and. 

 a long slope down to the drainage, which flows west of north. Here the 

 general dip of the strata is 30° NE. Near the lower end of the slope just 

 mentioned are four small folds of the strata, with axes trending about 



