THE REGION ABOUT GOLDEN. 85 



the one near the southern extent of the tract, the other for a mile and a 

 half "ii either side of Clear Creek. The former is of no particular interest 

 in the present discussion. The latter is attributable to two causes — one, 

 nondeposition at the base, due to a rise in the Archean floor and a conse- 

 quent shallowing of the sea at this point, the beds of the deeper water 

 abutting against this rise: the other, the disappearance from the top of the 

 series of the beds lasl laid down, including the Creamy sandstone and at 

 least LOO or 200 feet of the beds beneath. The linear extent of the disap- 

 pearance of the Creamy sandstone is probably somewhat under 1 mile, 

 and i> confined chiefly to the region immediately north of Clear Creek, 

 reaching to the south of it but slightly, if at all. In this interval the clays 

 of the Fox Hills are found in close proximity to the Red Beds, the former 

 conformable in strike with the Laramie sandstones above, the latter pur- 

 suing their usual trend, approximately parallel with the base of the range. 

 The upper member of the Trias presents nothing anomalous in its 

 occurrence until within a distance of about "2 miles north and south of 

 Clear Creek, when a rapid disappearance of its beds successively from top 

 downward i> found to occur as the center of the region is approached, the 

 limestones and associated beds at its base apparently reaching within a 

 short distance of the limit- already assigned for the Creamy sand-tones 

 below. An extremely important point in this connection is tin- fact that 

 this disappearance occur- where the overlying Jura is not only still present, 

 but where it maintains even the greater part of its thickness; it occurs, in 

 fact, between the dura above and the lower member of the Trias, the Red 

 Beds, beneath. The disappearance of this series of strata is most marked, 

 because more sudden, to the north of Clear ('reek and Gold Run, where. 

 within a distance of between one-half ami three-fourths of a mile, it has 

 decreased in thickness from 650 to 270 feet. The diminution in thickness 

 to the south of ( !lear < 'reek is also rapid, hut over this portion of the region 

 the Upper Triassic member i- not limited altogether by the dura above, hut 

 in part by the Dakota, with a discrepancy of at least 10° in their strike. 

 Farther to the south, where the dura is present in nearly its full thickness, 

 the variation in thickness of the Upper Trias is more gradual, but still to he 

 associated with the local phenomena of the region. 



