468 MEMOIKS OF THE CARNEGIE MUSEUM 



its former presence. This is apparently due to the hirge amount of pollution in 

 these streams, chiefly by water from mines. The pollution of the Alleghany River 

 near Pittsburgh, although bad enough from a sanitary standpoint, and due in the 

 first instance to sewage (Leighton, 1903, p. 122) does not affect the crawfishes, for 

 they are very abundant here, and the Ohio below Pittsburgh is rich in crawfishes. 

 But there are many smaller streams contaminated by the waste of coal-mines."' 

 Such streams are recognized at a glance by the precipitate of reddish and yellowish 

 sulphate of iron upon their bottoms, and are invariably without life. This is most 

 evident in the Monongahela drainage of southwestern Pennsylvania (Washington, 

 Fayette, and southern Allegheny Counties), and also in many smaller streams in 

 Butler, Westmoreland, Indiana, and Jefferson ( 'ounties, where coal-mines are abun- 

 dant. The worst conditions prevail in certain tributaries of the Monongahela, 

 in the Monongahela itself in the Lo3'alhaima below Tatrobe and the Kiskimin- 

 etas, and in Red Bank and Sandy Lick Creeks. The ( 'larion River is also with- 

 out crawfishes in Jefferson and Elk ( 'ounties, but this is due chiefly to pollution 

 by sewage from wood-pulp mills and tanneries (see above, p. 44o). In all these 

 cases it is evident that C. ob>!Curus once existed here, since remnants of it are left at 

 many places in some of the clearer and not polluted side streams. Since this pol- 

 lution of the streams by coal-mines is bound to increase, C*. ohscurus certainly will 

 disappear from other streams. As we have seen above it was on the point of dying 

 out in Sandy Lick Creek at Du Bois in 1905 (p. 443, footnote 58). Another case has 

 been observed in Fern-Hollow Run, Pittsburgh. In the fall of 1903 I found a 

 small number of specimens of this species left over in some pools once connected 

 with the run ; a sewer had recently been built here, discharging its jaolluted water 

 into the run. In subsequent years this species was not again seen, and has entirely 

 disappeared, as also from Nine-Mile Run, which receives sewage from \A'ilkinsburg 

 and Edgewood. 



It should be added that C. bartoni also is frequently influenced by the contamina- 

 tion of streams, but seems rather more resistant than C obsairus. In two cases this was 

 evident, namely, in Mahoning Creek at Punxsutawney, and in Slippeiy Rock Creek 

 at Branchton. In both cases the streams were only slightly polluted l)y mine-water, 

 and contained a certain number of specimens of C. burtoni, wliile C. obscurus was 

 absent. The latter existed at Punxsutawney in a pond connected with the stream, 

 and at Branchton in a smaller clear tributary, and consecjuently must have once 

 been present in the two creeks. 



A stream or river polluted in a certain part becomes relatively clear and pure 



" As to the chemical processes going on in the so-called " sulphur water," see Leighton, 1904, p. 24. 



