164 H. C. BRADLEY. 



there are many lakes set in clean rocky basins, and fed by 

 streams which leave little or no manganese stain on the rocks, 

 and which appear to be free from the masses of crenothrix. 

 In such lakes we have been unable to find mussels. In other lakes 

 in the same region where seepage through glacial drift was ap- 

 parent, or where the tributary streams flowed through such 

 drift, discoloration of the stones, evidence of the presence of 

 crenothrix, and the presence of the mussels seemed always to 

 go together. For example in the Temagami Reserve, Lake 

 Temagami itself is characterized by its clear water, and its clean 

 rock basin. In certain parts occur limited areas of drift sand 

 and gravel which are of insignificant amount. But though 

 the bottom afforded, where the lake washed such drift areas, 

 looked promising no mussels were found and the sandy stretches 

 were apparently free from crenothrix. To the north of Lake 

 Temagami are several lakes which lie in basins of glacial drift. 

 In Sucker Gut, for example, sand and gravel beaches are abun- 

 dant, the tributary stream flows through .many miles of drift 

 and carries enough manganese and iron in solution to stain its 

 stones and pebbles strongly brown and black. The sand itself 

 is stained with iron, and the brown slimy masses of crenothrix 

 are abundant. In this lake and its tributary stream we found 

 enormous numbers of small mussels wedged in thickly between 

 pebbles or projecting from the sandy bottom. The many obvious 

 examples in this region of the simultaneous presence of manga- 

 nese, crenothrix and mussels, or of the absence of all three is 

 probably more than a mere coincidence. We believe that more 

 careful examination would show thai the mussels require such 

 manganiferous food as crenothrix and that they cannot live in 

 \vaters where such food does not thrive. 



In growing the mussels in aquaria the specimens always carry 

 enough of the manganiferous organisms clinging to them so that 

 in a few days an abundant development of the bacteria results. 

 In this way several hundred grams of the dry organisms have 

 been obtained for analysis. Such specimens are mixtures of 

 a great variety of organisms and thus show large differences in 

 chemical content. The ash content of such plancton crops 

 vary from 24 to 76 per cent, of the dry weight ; the manganese 



