1911] May- Flies of Fall Creek, N. Y. 95 



PHYSICAL FEATURES OF FALL CREEK. 



The vicinity of Ithaca consists of two highlands between 

 which lies the basin of Cayuga Lake. The west highland 

 known locally as West Hill is a long regular slope, while East 

 Hill upon a terrace of which Cornell University stands, is fur- 

 rowed with gorges made by streams flowing downward to the 

 lake. On the gradual incline of the Eastern highland these 

 streams flow along as quiet meadow brooks, or broadening out 

 over stony beds are caught in a maze of ripply shallows, but on 

 reaching the steep terraces of the highland they plunge down- 

 ward through the narrow gorges by a succession of cascades 

 till they come to the plain below. These streams coming far 

 from their source and fed by many tributary waters are flooded 

 and turbulent in the spring, but gradually dwindle to mere 

 brooklets with trickling falls during the mid and late summer, 

 when the tributaries fail of their supply. Few of the main 

 streams become wholly dry. In March and April rich flora 

 and fauna spring from their banks and waters, while through 

 the dry season they supply enough water for the maintenance 

 of life and the reproduction of another generation. Fall Creek, 

 which bounds the Cornell Campus on the north, is a type of 

 these streams. 



About one mile east of the campus Fall Creek flows over a 

 broad nearly level bed thickly strewn with flat stones and rocks 

 which project from the water except at periods when the stream 

 is swollen. On one side the creek is bordered by a soft sandy 

 shore, on the other by a shelving ledge. Beyond this point, 

 where the ledge gives place to soft drift, there is a series of 

 permanent pools which mark the entrance of a small tributary 

 spring. A cross section of this upper portion of the stream 

 represents a variety of situations great enough to shelter widely 

 different types of May-fly nymphs. Clinging to the surfaces 

 of the stones in the mid current are the flat nymphs of Epeorus, 

 Iron, Ecdyurus and Heptagenia; clambering in the trash which 

 has collected between the stones are the nymphs of Ephemerella ; 

 on the sheltered surfaces or in the quiet border waters are Hep- 

 tagenias about to transform in company with Leptophlebia, 

 Siphlurus, and Ameletus; hidden in the sandy sweeps are Caenis 

 and Tricorythus and burrowing in the soft muck banks are 

 Hexagenia and Ephemera. Changing from this gradual descent 



