THE AUK: 



A QUARTERLY JOURNAL OF 

 ORNITHOLOGY. 



Vol. xxvi. July, 1909. No. 3 



THE GEOLOGICAL AND GEOGRAPHICAL RELATIONS 



OF THE LAND-BIRD FAUNA OF NORTHEASTERN 



AMERICA. 



BY SPENCER TROTTER. 1 



The antiquity of existing faunas is a problem beset with diffi- 

 culties and involved in obscurity. One who fares forth in this 

 quest will find few landmarks to serve him as a guide. No evi- 

 dence from fossil remains is forthcoming, for the deposits in 

 which recent animals have been buried are as yet incoherent muds 

 and silt, often beneath the waters of lakes and swamps and tidal 

 inlets. The remains of mammals and reptiles may thus have been 

 accumulating in many places over long periods of time, since the 

 beginning, at least, of post-glacial conditions. Undoubtedly the 

 soils of old forest floors and peat bogs and the mud of lake bottoms 

 contain a vast number of such remains, but it is altogether unlikely 

 that among these is any large proportion of the more fragile skele- 

 tons of birds. Even if they were preserved these remains, like 

 those of other creatures, would still be in inaccessible situations. 

 The clew to this history of faunas is to be looked for rather in the 

 distribution of living forms as we find them to-day; to facts re- 

 lating to the alteration of habitats, the invasion of new territory by 

 certain species, the recession from territory once occupied, and the 

 dominance and variety of forms of particular genera in various 

 localities. 



1 Read before the Delaware Valley Ornithological Club, Philadelphia, March 4, 1909. 



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