84 NORTH AMERICAN FAUNA. [xo. 16, 
for the southern Cascades and 7 for the northern Sierra. Of these 
distinctive specific types only 3 of the 7 Sierra species fail to reach 
Shasta, while all of the 8 Cascade species fail. 
The significance of these facts appears when the Boreal faunas of 
the mountains north and south of Klamath Gap are studied with ref- 
erence to their geographic sources of origin, as pointed out iv the next 
chapter. 
