1890 .] 
585 
[Leverett. 
the strata, their retention being due to the very dense nature of 
the beds which overlie the layers in which the salt water is pre- 
served. 
GLACIAL STUDIES BEARING ON THE ANTIQUITY 
OF MAN. 
BY FRANK LEVERETT. 
[ABSTRACT.] 
The paper called attention to the complexity of glacial problems 
whose solution has a more or less direct bearing upon the antiquity 
of man, and showed the necessity of long and careful observations 
upon various classes of phenomena by experts in the study of each 
class before a decision concerning the antiquity of man can be 
reached by geologists. 
As yet, scarcely any estimates upon the date and duration of 
the glacial period have been carried to a degree of accuracy suffi- 
cient to make it possible for conclusions of a high order to be 
drawn. Recent estimates indicate that the glacial period is less 
remote than was supposed by the earlier geologists. These esti- 
mates are based upon geological instead of astronomical data, and 
the tendency is to rely upon the former rather than upon the latter. 
Even careful estimates like those of Professor Gilbert on the falls 
of Niagara and Prof. N. H. Winchell on the falls of St. Anthony 
are not enough to fix with certainty the date of the close of the 
glacial period, as they themselves admit and even urge. Ad- 
ditional estimates and other methods of reckoning age besides 
by recession of falls must be brought into use to corroborate or to 
correct the results of this method. Evidence of age based on 
erosion seems to be the most reliable but it requires an expert of 
rare skill to interpret it. 
Since paleoliths have been found in both the newer and older 
drift it is important to determine their relative ages, a proceeding 
which will involve careful study in many lines ; and not only the rel- 
ative ages of the older and newer drifts but of the different por- 
tions of the newer drift should be determined. The great number 
of moraines in the newer drift suggests the lapse of a long period 
of time in their formations, and there is evidence that the line in- 
dicating the margin of the newer drift may not consist of a single 
