158 BOTANICAL GAZETTE [September 



In traveling from the north along the zone of hogbacks Ij'ing at the base of 

 the mountains southward, the traveler finds the mountain-slope directly west 

 of him falling lower and lower until it becomes an insignificant ridge, and 

 finally dies away in the plains. 



Passing around the southern end of the diminishing ridge the main 

 mountain-slope is found lying several miles to the west, and separated from the 



ridge by a baylike valley extending northward behind it The ridges 



are uplifted or anticlinal folds, the valleys depressed or synclinal folds, both 

 dying away southward into the flatness of the plains. 



The minor embayments due to echelon arrangement may be 

 made out only in a large scale map, but the major embayments at 

 the south end of the Rampart Range, the Pike's Peak highland, and 

 the Greenhorn Mountains can easily be seen in fig. i. 



A more detailed view of the typical land-forms and vegetation- 

 forms encountered in passing from mountains to plains traverses 

 the several north-south zones in the following order: first the 

 granitic foothills; then the transition zone of the mountain-front, 

 with its upturned ridges, its mesas and graded slopes, and in places 

 its plateau areas, buttes, and escarpments; and lastly the plains 

 themselves. 



GRANITIC FOOTHILLS 



The mountain plateau is in most places submaturely dissected, 

 the original upland level being represented only by the rounded tops 

 of the hills (fig. 3). Slopes and summits are thinly covered witTi 

 rock-waste. Occasional resistant dikes and ledges give craggy 

 exposures of massive rock, not covered by any soil or debris. Below 

 these, or on the sides of steeper ravines, are talus slopes of \-ariously 

 sized rocks, or slides of "granite-gravel."'^ Table I is a synopsis 

 of topographic areas of the foothills arranged as habitats, and, 

 correlated with these, the characteristic vegetation-types. Edaphic 

 conditions largely determined by topography (local position in 

 relation to surroundings, direction, amount of slope, and soil tex- 

 ture) have been discussed in the account of foothills vegetation (18). 



This two-column form of presentation is adopted as being 

 concise, as emphasizing relations between physiographic and onto- 

 graphic features (the environment and the environed) , and as per- 

 mitting a more comprehensive view of the whole complex and its 



3 Decomposed granite in small angular fragments. 



