86 NORTH AMERICAN FAUNA. [No. 16. 
one category, and the Sierra species (those south of Klamath Gap) in 
another, some additional facts are brought out which emphasize the 
widely different sources of origin of the distinctively Cascade species 
on the one haud, and the distinctively Sierra species on the other. 
Of the distinctively Cascade species, 25 percent are derived from 
mountains farther north, 12 percent are local types, 12 percent belong 
to transcontinental boreal types. and 25 percent to northwest-coast 
types. Of the distinctively Sierra species, 50 percent are specially 
developed local types, and 50 percent belong to types common to the 
Sierra and the southern Rocky Mountains. 
These facts point not only to the great antiquity and effectiveness of 
the Klamath Gap, but also to a former east and west continuity of 
range of Boreal species between the Rocky Mountains of Utah and 
Colorado and the Sierra Nevada of California, a distance of at least 
500 miles. 
