1898-99. | THE IROQUOIS BEACH. 41 
Germans ; but when this evidence is examined it proves to have little 
weight. Professor Ramsay Wright has been good enough to call my 
attention to the discussion of the whole question by Rudolf Credner 
in Peterman’s Mitteilungen.* According to Credner, who quotes 
Stimpson, S. J. Smith and A. E. Verrill, two forms apparently marine 
occur in Lake Superior, I/yszs refécta and Pontoporeta Hoyt; and five 
in Lake Michigan, the two just mentioned and three in addition, P. 
filicornis, Triglopsts Thompsont and T. Stimpsoniz. The late Professor 
Alleyne Nicholson found Pontoporeta affints in Lake Ontario.t The 
two most important genera, JZyszs and Pontoporeza, are tiny crustaceans 
which have been found also in numerous lakes in Scandinavia, and 
apparently easily accustom themselves toa life in brackish or fresh water, 
since they occur in such waters directly connected with the sea, and 
into which they have migrated. They or their eggs could readily be 
transported by waterfowl, and in fact might have passed up the canals 
to the upper lakes. Credner thinks that far too wide reaching 
inferences have been made from the finding in freshwater lakes of a 
very few species generaily supposed to belong to the sea; and that the 
decision that a given lake is a Relzktensee must be reached only after 
obtaining clear proofs of a geological character, since the fauna alone is 
a very uncertain guide. There are marine forms to be found in small 
crater lakes high up in the mountains, such as the Alban and Nemi 
lakes in Italy, where there is no hint that the sea has ever been in 
geologically recent times.t 
The fact that many freshwater shells occur in the interglacial beds 
of the Toronto formation is of some importance in this connection ; 
since the conditions under which these shell fish lived at heights of 140 
or even 220 feet above the present lake must have been similar to those 
of the great post-glacial lakes referred to above.§ 
At first glance the finding of marine fossils along the St. Lawrence, 
eg. at Montreal, 550 feet above the sea, seems to imply a lowering of 
the northeastern part of the continent sufficiently to bring the surface 
of Lake Iroquois down to sea level; but an examination of the curve 
illustrating the differential elevation of the Iroquois beach on a previous 
page shows that horizontality would be reached considerably above sea 
level. It is probable, however, as shown by Gilbert and Taylor, that 
the sea entered the basin of Lake Ontario at a later time and at a much 
* Die Reliktenseen, Erganzungshett No. 86 and 89, 1887. 
+ Ibid., No, 86, p. 65. 
{ Ibid., p. 107. 
§ Bull. Geol. Soc. Am., Vol. 10, p. 170, ete. 
