92 GEOLOGICAL SURVEY OF THE TERRITOEIES. 



eral features tlirougliout are rolling-bills upon the sides, witli low terrace- 

 forms near the streams, the latter being cut by many side-ravines. All 

 along upon the west is the great, rolling, wave like ridge of the Park 

 range, thickly timbered with i3iue. The broad head of the valley is a 

 gentle rise over into the North Park, the divide between the two i)arks 

 here losing its character of a defined ridge. On the east rises the high 

 table-land separating the valley fron^ the Upper Troublesome, but this 

 soon gives way to the low ridge separating the lower waters of the two 

 streams. Near the head of the valley is a prominent point called the 

 Upper Muddy Butte. Near its lower end, a similar isolated point, rising 

 at the. end of the low divide betfweenthe Muddy and Troublesome, and 

 called the Lower Muddy Butte, narrows the valley locally before it enters 

 the Grand. The general course of the valley may be taken as south 15° 

 or 20O east. 



The valley of the Blue resembles that of the Muddy in the terrace feat-- 

 nres along the stream, but it is a narrower and more strongly defined 

 valley, though by no means of the order of caSons. For the lower 

 twenty miles the general course of the valley is north 40°^ west. A few 

 miles from the mouth and 'on the east the Williams Eiver Mountains 

 commence to rise. The w^esteru face, or that sloping to the Blue, is much 

 steeper than the slope to the Williams Eiver. It tends to a terrace 

 form, being of strata gently dipping east. The outline is very sym- 

 metrical, rising in long slopes and gently-imdulating top to a central 

 point, and falling again in going south, but at twenty miles from the 

 Grand Eiver it abruptly joins a mountain region of a different class, 

 namely, the granitic masses west of the Gray Peak group, which line all 

 the remaining eastern side of the Upper Blue and quite change the char- 

 acter of its valley. For nearly twenty miles south of the Grand the 

 Park range on the west retains the same massive, evenly-rolling char- 

 acter as at the north. But suddenly it I'ises to one of the most rugged 

 ridges conceivable. 



The backbone of this ridge is near its western side, and trends about 

 north 40° east, but it is made up of numerous short eastern spurp, 

 which abruptly but pretty uniformly descend along a line nearly par- 

 allel with the main ridge. All these ridges are exceedingly sharp, and 

 rise to a very uniform and general level; though the highest point, Mount 

 Powell, is near the north end, and reaches an altitude of 13,285 feet. 



These sharp serrated ridges inclose a system of most profound gorges 

 and amphitheaters. The main ridge is broken through by the valley 

 of Ten-Mile Creek, but is immediately continued upon the south by a 

 ridge running southward to the Mount Lincoln group. 



GENERAL GEOLOGICAL DIVISIONS. 



The three general divisions to which attention was first called — the 

 plains, the mountains, and the park — the more salient topographical feat- 

 ures of which have just been described, are as natural geological divis- 

 ions as they are topographical ones, and will be considered in the three 

 following chapters in the order mentioned. The one next following, 

 Chaj)ter II, in the sedimentary rocks east of the Front range, presents 

 facts observed mostly along their western border, or near the mountains, 

 together with observations gathered from other sources. Chapter III 

 briefly gives some general results of observations among the Archsean 

 rocks which form the mountains, and though this study was made prin- 

 cipally upon the eastern mountain slope, yet the results appeared 

 equally applicable to any other of the crystalline areas observed by the 

 writer. Chapter IV deals with the general structure and distribution 

 of the rocks of the Middle Park. 



