I909-] FRESH-WATER FAUNA IN PENNSYLVANIA. 107 



the Allegheny itself is clear, and also forms a fine collecting ground 

 for the zoologist. This is especially true for the fish fauna and the 

 fauna of fresh-water mollusks. This good condition continues up 

 to the New York state line in Warren County. Of the tributaries, 

 Oil Creek is badly polluted at Oil City, where it falls into the Alle- 

 gheny, but it is pure at its headwaters. The intermediate parts have 

 not been studied by the writer, so that he cannot name the exact 

 spot where the pollution begins. It is due chiefly to oil refineries. 

 Tionesta Creek, in Forest County, is polluted by chemical refuse, at 

 least where it enters the Allegheny; the upper parts have not been 

 investigated. Brokenstrazv Creek, in Warren County, is in a fair con- 

 dition, but it belongs to the class of streams which improve during 

 their course : its headwaters are polluted by refuse from tanneries at 

 Cory in Erie County. Connewango Creek, in Warren County, which 

 brings the outflow of Chautauqua Lake in New York, is good. The 

 headwaters of the Allegheny in McKean and Potter Counties are 

 generally good, but there are some tributaries which are polluted, for 

 instance, Potato Creek, in McKean County (polluted by chemical 

 factories). Where Potato Creek falls into the Allegheny it is in a 

 very bad condition, but its size is not sufficient to influence the 

 Allegheny noticeably. 



6. The Lake Erie Drainage. 

 Of course Lake Erie itself is clear, and contains a rich fauna. ^** 

 In our state there are rather insignificant streams draining into the 

 lake, and they all have pure water, and, as far as they have been 

 examined, a well-preserved fauna. The largest is Conneaut Creek, 

 in Crawford and Erie Counties, which has been investigated at sev- 

 eral places by the writer, and found to be in good condition. The 

 only other streams known to the writer are Elk and Walnut Creeks, 

 in Erie County, which are also good. 



7. The Potomac and Susquehanna Drainages. 

 Only the headwaters of these streams or their tributaries are 

 situated in western Pennsylvania, and the investigations of the 

 writer are not very extensive in this region. 



^'' Our knowledge of the Lake Erie fauna is deplorably poor, chiefly so 

 with reference to the Pennsylvania shores. 



