THE BOULDER VALLEY LEGION. 123 



indentation midway the length of its northern face. This degree of devel- 

 opment is maintained as far south at least as the artesian well at the mouth 

 of the Lake Basin. The records of this well, which is 6 15 feel deep, show 



that the strata passed through were chiefly Laramie shales, with dip very 

 gently north-northwest. The How of artesian water at the bottom of the 

 hole indicates the presence there of one of the lower sandstones of the 

 Laramie. 



The northern extension of the svncline is traceable to the east-and- 

 west road, one mile north of the fortieth parallel. At this point it appears 

 only as the shallowest of depressions in tin- basal sandstones of the 

 Laramie. Midway between here and the Davidson mesa, ill the vicinity of 

 the "Burnt" Knoll, the broad and still shallow arch of the svncline is 

 locally compressed into a double trough with a median fold of low rise. 

 This is represented in the following- cross-section. 



IH'HNT KNOLL, 



Fin. 8.— Section tlir.mgh Burnt Knoll. A, B, Bas.il sandstones oi Laramie. Heavy black line = 

 Qoal seam. 



The southern extension of the svncline is easily traceable into the 

 Lake Basin and somewhat less definitely beyond to the slopes overlooking 

 Coal Creek; in this latter part of its course it> direction is a little more to 

 the west, in conformity with the system of rolls and fractures trending 

 N. 60° E. On the southern rim of the Lake Basin there is evidence of 

 another double fold of the general nature of that of Burnt Knoll, although 

 without its symmetry, the eastern trough in this case being distinctly 

 secondary in size and development to the western, which is plainly the 

 extension of the main svncline. In this southern portion of the svncline its 

 western side or rim is the upturned series of strata belonging to the moun- 

 tain uplift, the portion involved in it being that King south of South 

 Boulder ('reek: in the northern portion, on the contrary, in and north of 

 the Davidson mesa, opposite which the sharp mountain fold as usually 



