endlich.] VOLCANICS. 205 



rhyolite is reached, and, receding toward tehe higher portions of the re- 

 gion, extends for a vertical distance of 200 feet. After this a nearly level 

 area is traversed, while the ascent for the distance may amount to 100 

 feet. Above this, however, the trachytic beds are found in their regular 

 succession, at first the upper portions of No. 3, then the lower ones of No. 

 4. It is evident, therefore, that from this sideiio flow of rhyolites could 

 have occurred, and from any other side the possibility is precluded by 

 the geognosfic features of the surroundings. It is my opinion, therefore, 

 that the rhyolite occupied at one time a position very near the base of 

 the valley, and the outflowing basalt caused it to assume that in which it 

 is found at present. Inasmuch as this was the only locality where we 

 had occasion to observe two of the youngest volcanic eruptive rocks 

 together, my attention was led to the question whether this might not 

 be regarded as one of the greatest points of outflow, if not as the only 

 one. Subsequent evidence, derived from the stratification of the flows, 

 confirmed this Opinion, and I have arrived at the conclusion that near 

 this point the main outflow for the entire continuous volcanic area under 

 consideration occurred. In speaking of the stratification of the volcanic 

 rocks this point shall be further elucidated. 



Near one of two tributaries of Godwin Creek is Uncompahgre peak ' 

 (station 9), 14,235 feet above sea-level. The summit of this mountain is 

 formed by No. 3, and the lowest portions by No. 2. At the higher por- 

 tions of the peak the strata dip from 3° to 6° to the northeast, away 

 from the rhyolitic region that has just been described. The mountaiu 

 presents a bold appearance, and serves as a landmark for many miles. 

 Toward the southwest and west it slopes off more gently than toward 

 any other, but to the northeast presents a very steep appearance. A 

 small peak, to the south wevst of Uncompahgre, shows the identical strata, 

 lower, however, in elevation, and dipping in immediately the opposite 

 direction, to the southwest. This fact is of importance, as this peak is 

 nearer to the center of eruption. A number of high points are found 

 in the vicinity of Uncompahgre, none, however, reaching the same alti- 

 tude. Many of them present the same stratigraphical relations. 



Flowing in a northerly direction, w T est of Lake Fork, is Uncompahgre 

 Elver, rising near station 28. At that locality the strata of No. 4 have 

 reached a very good development, and in the ridge containing stations 

 27 and 28 the red stratum is particularly conspicuous. About four 

 miles north of station 28, station 29 is located, on the characteristic 

 bluish trachytes of No. 4, resembling closely those forming the higher 

 portions of Handle's peak. Similar to the occurrence of the white band 

 near the summit of that peak, we find one here of almost identical com- 

 position and locatiou. The trachytic rocks weather in scaly fragments, 

 sometimes of considerable size but of small thickness. From that point 

 the higher numbers of trachyte extend northward in narrow ridges, but 

 little cut by lateral drainage. A tendency to columnar structure pro- 

 duces along the steep sides of these elongated ridges numerous pin- 

 nacles, from a distance apparently small. They reach considerable ver- 

 tical dimensions, however, and may be compared to the ornamental spires 

 of Gothic architecture. Added to the effect produced by their form, the 

 colors they exhibit are an additional factor. Near the headwatersof some 

 oftheUncompahgre's tributaries is one peak that attracted attention by 

 its singularly regular form, long before it was reached — Mount Sneffels, 

 reaching an altitude of 14,162 feet. It was our station 33, and 

 proved to be an interesting point. Horizontally stratified, or with 

 an imperceptible dip of the strata, this mountain towers far above 

 its surroundings, rising more than 7,000 feet from the lower country 



