MORGAN. ] INDIAN MIGRATIONS. 197 
That the original ancestors of the principal historic tribes of Mexico 
once inhabited the San Juan country is extremely probable. That the 
ancestors of the principal tribes of Yucatan and Central America owe their 
remote origin to the same region is equally probable. And that the Mound 
Builders came originally from the same country, is, with our present knowl- 
edge, at least a reasonable conclusion. 
Indian migrations have occurred under the influence, almost exclusively, 
of physical causes, operating in a uniform manner. These migrations, 
involving the entire period of the existence here of the inhabitants of both 
American continents, will be found to have a common and connected his- 
tory <A study of all the facts may yet lead to an elucidation and explana- 
tion of these migrations with some degree of certainty. The hypothesis 
that the valley of the Columbia River was the seed-land of the Ganowanian 
family holds the best chance of solving the great problem of the origin and 
distribution of the Indian tribes. 
