2 



mountains become high and rugged; the west is hilly and the 

 southeast and northwest occasionally so, but very frequently 

 level. 



The only lake of importance is Lake Erie, forming 

 the northwest boundary for about fifty miles. On the east- 

 ern border, the Delaware River flows south and empties into 

 the Delaware Bay, being joined by the Schuylkill below 

 Philadelphia and at Easton by the Lehigh; each tributary is 

 about one hundred miles in length. Farther inland the 

 Susquehanna, the largest river in the state, enters Pennsyl- 

 vania from New York and, flowing southerly, crosses the 

 entire state, dividing it into two unequal parts. Its 

 principal tributaries are the West Branch and Jtmiata from 

 the west and the Swatara and Conestoga from the east. The 

 Ohio, which is formed by the union of the Alleghany from 

 the north and the Konongahela from the south, drains the 

 western part of the state, having about fifty miles of its 

 course in Pennsylvania. The Alleghany extends to the north 

 for three hundred miles, while the Monongahela stretches 

 away for two hundred miles. 



With such a variety of country and topographical 

 conditions, it is little wonder that the number of birds 

 summering in this state is large. The higher Alleghanies 

 carry south with them many birds that typically breed much 

 farther north, while the mild climate of the southern 

 counties brings north birds typical of the sunny south. 



