1907] 



YOUNG— FOREST FORMATIONS OF COLORADO 



323 



depth.3 These readings are of course not entirely satisfactory in 

 determining the soil water available for the trees, with their roots 

 extending to a depth of many feet; but the deeper sample probably 



Fig. I. — Castle Rock in Boulder Canon, altitude 2250™; in the foreground and 

 to the right is seen the Populus angustifoIia-Salix Nuttallii formation; scattered 

 over the hills are Pscudotsugas and Piceas. 



gives a fair basis for comparison of habitats in this respect 



It is 



exceedingly difficult in any extended investigation to carry a geotome 

 which will reach a depth of several feet. The soil samples obtained 



3 Exceptions to these depths will be noted below. 



