86 GEOLOGl OF THE DENVER BASIN. 



i'ii>- jin.i.- -No extraordinary discrepancy in strike or in general relations 

 between this formation and either the underlying or overlying one is 

 apparenl until upon near approach to the confines of the region presenting 

 the anomalies just described for the Trias, Any decrease in the thick- 

 ness of the Jura beyond is little more than is usually me1 with from poinl 

 in poinl along the range, From aboul a mile south and a mile and ;i half 

 north of < !lear < 'reck, however, the beds of the formation disappear in rapid 

 succession us the center of the region is gained. Their strike is, moreover, 

 al variance with the formations both above and below; in the southern 

 pari ii is iu notioeable contrasl with thai of the Dakota, being some 10 

 or 15 to the easl of the latter; in the northern portion no1 only is the 

 same discrepancy probable between these two formations, but an equal 

 one also appears between the beds of the Jura and those of the Trias 

 below. The thinning of the Jura is in pari probably due to the absence 

 of some of its lower beds, while the cause of its sudden and final thinning 

 is found in the rapid and successive disappearance of, first, its upper beds, 

 followed in turn by those lying beneath. 



rhi DakoM As ascent is gained ill the series ol lol'ma t ions, the region ot 



anomalies becomes more and more extended in north and south direction-. 

 The Dakota begins to display irregularities as far south as the northern 

 end of the high hogback just south of Coon Grulch, and in the north 

 al the southern end of the chain of hogbacks north of Grolden. The 

 noticeable points in the behavior of the southern half of the formation 

 are, first, the disappearance of the characteristic hogback; second, the 

 gradual decrease in thickness, which the outcrops of the remaining portions 

 show in be both from above and from below, the fire-clays in the middle ol 

 the formation being the last to disappear, as e> idenced a1 the bluffs of both 

 Clear ('reek ami Gold bun: third, the discrepancy in strike between this 

 formation and those below and above, its l>e<ls in the region of more 



pr tunced irregularity lying across the edges of the former, and abutted 



from above b> the ends of the successive strata of the Montana group 

 throughout much of their line of contact: finally, frequent changes in 

 the strike of its beds over the central portion of the affected area, which 

 changes are not paralleled by corresponding ones in the prominent sand- 

 stones at the base of the Laramie, lying hut a short distance to the east. 



