CONGLOMERATES OF WET MOUNTAIN. 265 



sandstones and conglomerates of prevailing red color, exposed by the erosion 

 of the Arkansas river after it assumes its eastward course, which occupy a 

 corresponding stratigraphical horizon, without, however, showing any evi- 

 dence of unconformity with the beds below. 



Wet Mountain Island. — The Saugrede Cristo mountains, from the Arkan- 

 sas river southeastward to the head of Huerfano park, must have formed the 

 western shore of the Wet Mountain island at this time, their relative posi- 

 tions as mountain and valley having been then the reverse of those which 

 exist now r . This range opposite Silver Cliff is largely made up of an immense 

 thickness of conglomerate whose pebbles, of all varieties of Archaean rock, 

 cannot have suffered any very prolonged attrition, for they not only con- 

 sist of relatively soft material, but are sub-angular and often in immense 

 blocks over 25 feet in diameter which could not have been carried very far. 



It seems probable that these conglomerates extend the entire length of the 

 range, since they have been observed by Stevenson on its eastern flanks, ex- 

 tending beyond the state line into New Mexico, where they contain limestone 

 pebbles associated with those of Archaean rocks. He gives them an aggre- 

 gate thickness at one point of about 6,000 feet. 



It is a question whether the material of which they were composed was 

 derived from the Wet Mountain island or from some land-mass to the west- 

 ward which has now disappeared. The fact that on the east flanks of the 

 Wet Mountain island no beds at all corresponding to them in thickness or 

 coarseness of material have been found, would favor the latter conclusion. 



The section at Canon City shows a thin limestone conglomerate or breccia, 

 made up of slightly rounded fragments, immediately and unconformably 

 overlying the lower Palaeozoic beds, and succeeded by a few hundred feet of 

 beds mostly of reddish arkose material with a few limestone pebbles near the 

 base. The characteristic red sandstones of the Trias have either been eroded 

 away or are overlapped and concealed by the unconformable Jura-Dakota 

 beds. Two exposures of Triassic beds are indicated on the Hayden map 

 south of this point along the eastern flanks of the Wet Mountain range. 

 Elsewhere they have been overlapped by the unconformable Jura-Dakota 

 series. In like manner, south of Huerfano park, along the east front of the 

 Sangre de Cristo range, the Jura-Dakota beds abut directly against Archaean 

 or Carboniferous rocks, and no Triassic beds have been recognized, except 

 near its southern extremity. 



San Juan Island. — In the San Juan region, elevation and erosion is shown 

 to have taken place by the fact that on its northern flanks a slight angular 

 unconformity is observed between the lower Palaeozoic series and the coarse 

 grits, sandstones and shales that were deposited during the later Carbon- 

 iferous. This discrepancy of angle was not observed on the southern slopes 

 of the mountains along the Animas canon, but of the areas represented there 



