528 REPORT OF STATE GEOLOGIST. 



ZOOLOGICAL AREAS. 



Geographers have attempted to divide the world into zoological re- 

 gions in accordance with the harmonic distribution of certain typical 

 forms. These zoological areas have not been very accurately denned. 

 They may be termed the different divisions of the sea of animal life, 

 with its tides, currents, varying temperature and depth, two areas 

 meeting as land and sea, each with irregular shore lines and deeply 

 indented coasts, the boundaries continually changing as barriers in 

 one direction are overcome, and in another a different coast configura- 

 tion appears. 



Indiana is included entirely within the Eastern (Atlantic) faunal 

 province, and while it is within the limits of the Carolina fauna of 

 Mr. Allen, the southern portion contains so many birds that are dis- 

 tinctive of the Louisiana fauna (Austroriparian Province of Professor 

 Cope) that it has been thought it should be referred to that district. 

 According to Dr. Merriam's provincial classification, almost all of 

 Indiana is included within the upper Sonoran Zone. The Transition 

 Zone appears in the northern part, while the extreme southwestern 

 portion is included in an arm of the lower Sonoran Zone. 



BIRD MIGRATION. 



The migratory instinct is one of the wonders of nature. The origin 

 of migration seems to reach far back into the unwritten history of the 

 past. According to geological testimony, in the earlier ages of the 

 earth's history a warm climate existed almost to the North Pole. 

 Then neither lack of food nor the consequences of rigorous winter 

 compelled the birds to leave that favored region. With the changing 

 of conditions by which the circumpolar area became colder, then ice- 

 locked and finally the limit of ice extended far to the southward, the 

 birds were forced to more congenial lands. With the winter they 

 sought warmer climes, and as the summer approached they sought to 

 return to the ancestral home. Finally the southern limit of the ice 

 sheet was reached, and it began to recede. With its recession the birds 

 were enabled to reach higher latitudes, and in time, when the frigid 

 area reached its present limitation, there was left for our solution the 

 problem of the migration of birds. This habit is not the acquirement 

 of any one bird, but is the influence of the experience of many gen- 

 erations of birds extending through long ages of time, an inherited 

 desire to seek nesting sites near the old home of their race. 



With what regularity do certain forms leave their summer homes in 

 the temperate and frigid realms and traverse the great expanse of plain 

 and wood and ocean to far within the tropics, there spending the 



