I JO NEW YORK STATE MUSEUM 



slightly saline waters of the upper Baltic, are represented here. 

 It is quite possible that all or part of these forms were carried in 

 by rivers; but the situation of Pakenham Mills near the western 

 limit of known marine fossils is significant and in favor of brackish- 

 water conditions there, and consequent adjustment of the fresh- 

 water forms to this condition. Also, as noted above, the only 

 marine shell found is Macoma groenlandica, which is 

 now found farther up in the estuaries than most others. 



There is evidence of freshening of the sea westward. In the region 

 west of the fossiliferous beds, at higher levels, are beachlike deposits 

 of sand and gravel and also stratified clays resembling the Leda 

 clay which are believed by some to be of marine origin, but by others 

 (see Coleman, p. 136, 145) to be of fresh-water origin. Coleman 

 says: " That the old sea level at 350 feet continued into the Ontario 

 basin, and may even have reached its western end seems very 

 probable, and the fact that marine fossils are very abundant east 

 of Brockville, but have never been found to the west, may be accounted 

 for by the narrowing of the lower end of the basin forming a strait 

 not very much wider than the present river and only 100 feet deeper; 

 so that Niagara and the other rivers flowing into Lake Ontario 

 were able to keep the waters fresh, or at least only brackish, in 

 spite of their communication with the enlarged Gulf of Saint Law- 

 rence " (Ref. cit., p. 136). 



Part 2 Dwarfing of Species and Other Modifications 



Dwarf faunas may be divided into two classes: (1) " faunas 

 where the individuals are of smaller size than that to which the 

 species grows under normal conditions; this is the result of an 

 abnormal habitat; (2) faunas where all the individuals are small 

 but of the normal size of the species; in this case some selective 

 action has weeded out all the large and heavy species, leaving a 

 dwarf but not stunted fauna. Dwarf faunas usually include repre- 

 sentatives of both classes " (Shimer, p. 490). This, from the data 

 gathered, seems to be true of the Champlain Pleistocene fauna. 

 The dwarfed character of this fauna is well shown by five species: 

 Macoma groenlandica, Saxicava rugosa, 

 Mytilus edulis, Mya arenaria, Yoldia arctica 

 (see plates 1-3). Through the kindness of Doctor Pilsbry, I 

 have obtained for comparison recent specimens of these species, 

 in addition to those in the State Museum. 



It is well, perhaps, to give approximately some idea of the numbers 

 of individuals of the different species, upon which comparisons 



