Review of Recent Geological Literature. 375 
some land and fresh water bivalves and univalves. For example: 
Ostrea diluviana Linn, from the Turonian of Europe, an Ostrea to which 
the same name has been given from the Lower Cretaceous Comanche 
series of Texas, 0. barrandei Coquand and O. dilleri White from the 
Upper Cretaceous of New Jersey and California, respectively, are all so 
closely related in form that their differences are not greater than the 
individual variations usually seen in the species of this genus. The as- 
sociated forms are all distinct. Several other examples are cited among 
Ostreidae, Aviculidte, Unionidae and other families, in some of which the 
forms are separated by much greater time intervals. 
The method of treating such forms will depend largely on the charac- 
ter of the work that the paleontologist has in hand and on the relative 
importance that he gives to the geological and the biological sides of his 
subject. If the investigation is purely biological without reference to 
geographical or geological distribution, these closely related forms are 
naturally regarded as belonging to the same species and are called by 
a single name. If, on the other hand, fossils are studied as an aid in 
describing and characterizing geological formations, and a given for- 
mation yields a fauna made up of species peculiar to itself with 
the exception of a few such forms as those under discussion, it is held 
to be admissible to treat the entire fauna as distinct and to give a new 
name to each species. 
It is believed that this method of treatment will give better and more 
direct results in the classification of the formations of this continent, 
and in their ultimate correlation with those of other continents, than 
would one in which biological ideas predominate. The synonyms that 
may be thus introduced are regarded as of little consequence compared 
with the resulting advantages. 
Glacial Lakes in Canada. By Warren Upham. Bulletin of the 
Geological Society of America, vol. ii, pp. 243-270 ; March 5, 1891. A 
glacial lake, according to the use of the term in this paper, is a body of 
water bounded in part by a barrier of land-ice, as the Merjelen see of 
the present day and lake Agassiz in the closing stage of the Glacial 
period. The evidences of the former existence of glacial lakes', pent up in 
valleys and basins which had descending slopes toward the ice-sheets 
during their final recession, are comprised in five classes : (1) channels 
eroded by streams outflowing from the glacial lakes across the present 
great lines of watershed; (2) low cliffs eroded along the lake shores, 
commonly consisting of till ; (3) beaches of gravel and sand, often reach- 
ing continuously in a wave-formed ridge along a distance of many miles; 
(4) deltas of gravel and sand, brought into the edge of the lake by 
tributary streams; and (5) finer lacustrine sediments, brought mainly by 
the same tributaries and spread over the lake bed beyond the deltas, but 
in part supplied by wave-erosion of the lake shores. 
The principal glacial lakes of Canada are noticed in geographic order 
from west toeast. In British Columbia the "White Silts," described 
by Dr. George M. Dawson as occurring up to altitudes of 2,300 to 2,700 
feet, and by him referred to marine deposition, are regarded by Mr. 
