[27] 



In respect to geological formation, the Tidewater is a Tertiary 

 region, the Middle and Piedmont divisions are mainly Eozoic or 

 Primary, portions of the former especially, being, however, 

 Mesozoic. On its eastern slope, usually including its summit, 

 the rocks of the Blue Ridge resemble those of the Piedmont 

 region (epidotic), on the western, those of the Valley. The 

 Valley is made up of Cambrian and Lower Silurian rocks 

 mainly limestones. 



The Appalachian country chiefly consists of Upper Silurian 

 and Devonian rocks with some Carboniferous and Sub-carbo- 

 niferous, while nearly the entire area of the Trans-Appalachian 

 region is Carboniferous. 



In the Tidewater region, the mean annual temperatvn"e ac- 

 cording to locality is from 55 to 65 F. ; in Central Virginia 50 to 

 60 ; in the Mountain region 40 to 55 ; in Western Virginia 50 to 

 60. 



The physical and topographical features of the Virginias are 

 thus so varied that the number of birds found is necessarily large. 

 The noble estuary of Chesapeake Bay and the large rivers which 

 empty into it, the islands along the eastern shore of Accomac 

 and Northampton counties (though now largely depopulated 

 of their feathered inhabitants in comparison with former times), 

 the Great Dismal Swamp and waters of Princess Anne County 

 furnish feeding grounds for Ducks, Geese, Swan, the numerous 

 varieties of Waders, and the Gulls, Terns and Herons ; the well 

 wooded regions of eastern Virginia are filled with land birds 

 while the Valley and West Virginia offer still other features 

 which influence the bird distribution, and upon the high moun- 

 tain tops birds are met with which in summer are confined to 

 that region. 



As the Flora of a country bears an intimate relation to its cli- 

 mate and fauna, brief mention may be made of the botanical 

 features of the Virginias. It is more or less intermediate in 

 character between that of the Nortliern and .Southern Atlantic 

 States and east of the Blue Ridge, with the exception of the 

 warmer south-eastern portion, is similar in great measure to that 

 of the District of Columbia, which has been very fully investi- 

 Sfated.* 



•Bulletin of the U. S National Museum. No. 22. 



