• COLOKADO AEOHiEAN BODY. ' 21 



Thompson also empties into the South Platte about 10 miles above the 

 Cache la Poudre. 



Most of the waters from Long's Peak, however, drain into the Saint 

 Vrain's Creek, branches of which nearly encircle it on all sides. 



A vigorous growth of coniferous forests, including several species, 

 among them Pinus ponderosa and Ahies Engelmmmi, cover the greater part 

 of the long eastern slopes. In the region of Monitor Peak and the broad 

 level country to the north, reaching nearly to the Laramie Plains, the forests 

 are quite dense, and have furnished large supplies of timber in the form of 

 railroad-ties. 



The limit of timber growth from Long's Peak northward may be placed 

 at 11,000 feet above sea-level, although there doubtless are a few exposed 

 localities where it does not quite reach that elevation. 



Geology. — The main geological features of the Laramie Hills continue 

 southward along the Colorado Eange, which consists of an elevation of 

 highly crystalline rocks of Archaean age, flanked by a series of later sand- 

 stones and limestones. In the latter case, however, the sedimentary beds 

 occupy a much inferior position than they do to the north. They seldom 

 appear along the flanks of the foot-hills higher than 500 or 600 feet above 

 the Plains, while the Archaean formation rises more than as many thousaind 

 feet, and occupies the broad area between the Plains and the Medicine Bow 

 Range. 



But while this higher region presents many points of resemblance with 

 the Laramie Hills, the structure is in detail so much more complicated that 

 a very considerable time would be required to work out with any degree 

 of accuracy the stratigraphical relations of the different beds. The task 

 would also be increased from the fact that all structural lines are frequently 

 wanting, or difficult to follow, over many extended areas. It may be said, 

 however, although with considerable hesitation owing to the Hmited ob- 

 servations in the field, that, in its general structure, this portion of the range 

 presents a broad anticlinal axis, accompanied by many secondary folds and 

 plications of strata between the summit and foot-hills. Although there are 

 localities of westerly dipping beds along the east slope, they are usually 

 quite steep, with the appearance of being limited in extent, while by far 



