OURAY UNCONFORMITY 459 



almost due north, and it is plain that a monoclinal'fold is necessary to 

 bring the top of the Hermosa to the horizon it occupies beneath the Tri- 

 assic conglomerate east of the river. This fold, of general north-south 

 axis, must have been situated where the present canyon of the river is 

 cut, and hence is not visible. The greater fold, soon to be described, 

 probably obscures this canyon plication in its northward extension. 



The northward dip of the strata below the Trias is disturbed by a sharp 

 monoclinal fold with northwest-southeast axis and northerly pitch, which 

 crosses the Uncompahgre canyon shortly below Ouray. The visible por- 

 tion of this fold is mainly within the unfossiliferous Red beds, and as 

 the Triassic and overlying strata are not affected by it the relative age of 

 the movement is plain. The fold brings 1,000 feet or more of beds of 

 deep red color to light between the Triassic and the Hermosa and shows 

 the magnitude of the unconformity in striking manner. On account of 

 local topographic features the unconformity is less evident above this 

 fold than in the cliffs near the amphitheater. 



Plate 85 shows the fold on the west side of the river back of the Amer- 

 ican-Nettie mill. The diagram opposite shows where the line of the un- 

 conformity runs, and an observer stationed at about the Triassic horizon 

 on the eastern side of the river, as, for instance, on the bench where the 

 workings of the Bright Diamond mine are situated, can readily perceive 

 that the Dakota and La Plata limestones do not take part in the sharp 

 fold, and at some points the actual unconformity can be clearly seen. 

 From the cliff adjacent to Oak creek to Corbett gulch the Mesozoic strata 

 dip at about 6 degrees. 



To the north of Corbett gulch (see plate 85) the Paleozoic and Triassic 

 beds come into such close approximation to conformity that careful obser- 

 vation is required to detect discrepancies in strike and dip which actually 

 occur. There are minor, gentle, pre-Triassic folds in the Paleozoic beds, 

 but other similar structures are evident in which the Mesozoic strata take 

 part and the unconformity is thus easily overlooked. At about 7 miles 

 north of Ouray the Triassic and lower Jurassic (La Plata) beds dip beneath 

 the alluvial plain and are not again exposed in the Uncompahgre valley. 

 Very good outcrops of both these formations occur on the eastern bank, 

 and near where a diabase dike cuts them, but little above the floodplain 

 of the valley, the basal conglomerate of the Trias contains bone fragments 

 and some belodont teeth. This is at about 100 feet below the La Plata 

 sandstone. Their presence at this point was first noted by H. S. Gane 

 in 1895. 



DESCRIPTION OF FORMA TIONS 



Cutler formation — Selection of name. — The preceding account of the 

 Ouray unconformity will have made plain that no further reason 



