132 MOLLUSCA. 



on the north shore, there is a long, narrow lake, Long Lake, which is 

 about nine hundred yards long by sixty wide, and is very shallow, no- 

 where reaching a depth of over three feet. This lake has apparently 

 been formed in the same manner as the sand pools and marshes in 

 partially protected places where the water is very shallow for some dis- 

 tance off shore, that is, by a barrier beach having been thrown up paral- 

 lel to the beach during storms. Then, as the beach moved north, grow- 

 ing out in this same way, a sand dune would be blown up between the 

 lake and the Bay, and the present relations would be established. The 

 long narrow shape of the lake and its shallowness accord with this view; 

 but these relations might also be explained by the presumption that the 

 lake was formed by the drainage water collecting between parallel sand 

 dunes. It seems probable, indeed, that both methods have contributed 

 to the formation of this lake. (Pis. XII, XIII a.) 



The lake has a firm, sandy bottom and has the characteristic zone of 

 Scirpus americanus along the edge. The main portion of the lake has 

 little vegetation besides this sedge and a few patches of the yellow 

 water-lily (Nymphoea advena). The extreme east end, however, has a 

 soft peaty bottom composed of decaying vegetation. (PI. XII b.) 

 Here the yellow water-lilies and a small sedge, probably Carex fiUformis, 

 almost hide the water. The water thruout the lake is cpite strongly 

 impregnated with iron. 



A few specimens of Planorhis trivolvis, P. exacuous, and of a small 

 form of Musculium secnris were found on lily-pads and among sedges 

 in the sandy, western portion of the lake. In the mucky-bottomed 

 east end, the first species was found in much greater abundance on the 

 under-side of lily-pads; and among and on sedges, about six inches from 

 the bottom, the small form of Miisculium securis was also collected in 

 great abundance. 



T^e eastern end of this lake is being filled in by the deposition of plant 

 material, the western end by sand blown in from the dunes on l)oth sides. 

 The ultimate end of either process will be the destruction of the lake. 

 The eastern end will probably become a peaty swamp, while the western 

 end may become dominated by the aquatic vegetation as the lake be- 

 comes shallower and better protected by the surrounding growths, or 

 it may be filled in by the sand alone. 



10. Deep lakes , south side of Sand Point. A few rods in from shore, 

 along the south side of Sand Point, are two lakes and several marshes 

 where similar lakes have been. These two lakes are known locally as 

 Mud and Orr Lakes. They are neither of them long, narrow lakes of 

 small depth, as is that described under habitat nine, but are irregularly 

 oblong in shape, are Cjuite deep and have a soft, mucky bottom. These 



