THE FOOTHILL VEGETATION 111 



growth. The species has a wide range of adaptability. While 

 it grows with the greatest luxuriance in the region of heavy 

 rainfall west of the Cascades it also occupies the outposts of 

 forest vegetation bordering the dry prairies in the Rocky Moun- 

 tains and adjacent plains. In the latter situations, however, 

 its inferior size and form indicate the hardships to which it is 

 subject. In another way also is it inferior to the pine in the 

 Rocky ^Mountain region where it succumbs frequently to the 

 attacks of Razoumofskya Bouglasii. As these negative qualities 

 are only relatively of importance, the Douglas spruce is remark- 

 ably well fitted for successful competition and becomes locally 

 here and there in the Rockies, and far more extensively farther 

 west, the dominant species. Its geographic range is greater 

 than that of the western yellow pine. 



The extensive distribution of Juniperus scopulorum, an- 

 other of the Transition, or foothill species, seems largely to be 

 the result of its rugged adaptability to adverse soil conditions, 

 both as to moisture and other qualities, and to the effective 

 means of the distribution of its seeds by birds. It is however, 

 never abundant to the extent of forming forests, but appears, 

 in the few places where it is pure, in widely open stands. 

 This fact is perhaps associated with the relative paucity of its 

 seeds and to its exceedinglj' slow growth. It is nevertheless a 

 species resistent to a wide range of temperature and apparently 

 suited to many different soils. 



It is quite evident that the grassy slopes of this region have 

 not been forested since pre-glacial times. The condition about 

 Missoula furnishes an interesting study in this particular. The 

 city is built upon a gravel plain at one time the bed of a sup- 

 posedly Pleistocene lake; on all sides to the hight of 1,000 feet 

 above the city are clearly marked shore lines of the ancient 

 sea. For miles these may be traced horizontally and they mount 

 one above another in a close succession of slight undulations. 



The lines of these shore terraces lie chiefly in loose materials, 

 gravels, soils or broken rock. In view of the effects of large 

 roots upon such materials and the minor displacements con- 

 sequent in the course of time, it seems impossible that forests 

 could ever have occupied these slopes without obliterating the 



