QRAT AM) BOOKEB OS THE ROCKY MOUNTAIN FLO 3 



Our sketch meat be, Uke onr observations, a rapid and cm wrj recoil' 

 Mtorawe, noting some features which arrested onr attention, drawing 

 e comparisons, and suggesting inferences which seem to us probable. 

 Tlif ]»li raphy of the temperate portion of the North American 



inent, in broad outlines is evidently this : An Atlantic forest i« . 

 a Pacific forest region ; and, between the two, the wide interior, main!; 

 non-1 prion — the special Bubjectof our essaj ; a regiou n<>t eas 



b nor to describe succinctly, but of which the eastern half is a 

 Hess plain, gradually and evenly rising, bo that its western margin 

 out 5,000 feet above the sea-level; then a mountain i»«*l t . the high* 

 est ridges and peaks of which rise from 1 1,000 to 14, 100 feet ; then, shut 

 out from moisture by these mountains on the east and the Sierra mi the 

 an arid interior district of f lains, at an average of 5,000 feet 

 above the sea. This la mainly desert, and is traversed bj many mount- 

 ain ranges, generally of north and south direction, and reaching an ele- 

 vation of £,008 or 10,000 feet, or rarely higher. This whole interior, of 

 mile- breadth — like other meat interiors not very exceptionally 



marked by the scantiness or absence of arboreal vegetation 

 and <>t" rainfall, the former being in great measure dependent on thelat- 

 [ts plains are treeless except along water-courses; the mountains 

 trees along sheltered ravines and <>n their higher slopes, upon 

 which there is considerable condensation of moisture; but, whenever 

 they rise to a certain height (about 11,000 feel in latitude.;;" to 



ire woodless from cold and other hardship attending elevation, 

 although they enjoy an abundant condensation of moistu ly in 



lOWi 



The Rocky .Mountain region may be therefore divided vertically into 

 botanical distric 



1. An arid and woodless district, which occupies far the part 



a area. 



A wooded district, in some pi ices covering, in others locally adorn- 

 • he mountain slo] 



lpine unwooded district amove the belt where tre< Bui 



lie plaoeSfSlopes woodless from dryness merge into tracts woodless 

 i <•«>].]. do proper forest belt interveni 

 These three botanical distri< separately investigated. 



The smallest in area — since it is restricted t<» mountain summits and 

 the leasl peculiar, is — 



1. — 'i'jii. A i.i'i.M !;, 



tanicallj the alpine n aone in the northern 



bemispbe southward p I ions of ard ic \ < 



in the boreal parts, but more and more mixed with special 

 r latitude special typ< \ a part of the flora which is 



coutinent iu tho • 



