channel. Actually it is one-half mile from the en-i. 



Starting with Station 251^, at the channel, we note again that 

 there were 5oU Tubificidae and 68 Hexagenia per square meter, indicating 

 light pollution. At Station IIC, one mile distant in a southeasterly 

 direction, the single sample showed a total absence of Tubificidae, and 

 the presence of l62 Hexagenia per square meter. At Station 109, two 

 miles from the channel, the tubificid worms were also absent, and the 

 mayflies were more abundant than at Station 110. Again at Station 107, 

 four miles from the channel, no worms were found, but the mayflies were 

 less abundant than 'at the previous two stations, a circumstance which 

 is readily explained by the predominance of sand over mud in the bottom 

 material. Three samples were taken at Station 105, located six miles 

 from the channel. Here the bottom was predominatly mud rather than sand, 

 and the difference is reflected in the greater number of Hexagenia. 

 Tubificidae were present in traces. It is apparent that there is no 

 evidence of pollution in the few samples taken in this series. 



Further evidence of the fact that there is no eastward extension 

 of pollution along the south shore is given in Table 90, This table 

 gives the results obtained at six stations arranged in two series running 

 out from the shore asdiown in Figure 23. Tubificid worms were not found 

 at any of the stations, and a fair number of Hexagenia was found at the 

 stations where good samples could be taken. There need be no hesitation 

 in assigning this area to the zone of clean bottom. The di-viding line 

 between it and the zone of light pollution would be placed, then, between 

 Stations 25ii and 110, 



The three stations in the northwest series (Table 89) are 

 represented by single samples in 1930, At Station 112 it was impossible 

 to take a quantitative haul because of the bottom material, which was 

 composed of hard clay overlain by sand and pebbles. It should be added 

 that the single sample recorded in the table does not represent the 

 total effort expended in an attempt to obtain a representative sample. 

 At this station, and at many others to be recorded later, numerous un- 

 successful hauls were made before the attempt was abandoned. The sample 

 recorded for Station 112 was the final one. Enough of the bottom was 

 taken to show that there was no accumulation of organic debris, and it is 

 probable that few organisms were present. The single sample taken near 

 this point in 1928 showed 86 Hexagenia per square meter and a consider- 

 able number of chironomid larvae, but no Tubificidae, 



At Station llli, three miles from the channel, the bottom was 

 composed of sand with an admixture of mud'. The small number of Hexagenia 

 can be explained by the small amount of mud in the bottom material. The 



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