Fepruary 23, 1912] 
must be regarded as an event of Pleistocene time. 
The paper was discussed by W. W. Atwood and 
Wm. M. Dayis. 
Fossils of Lower Limestone of the Steep Rock 
Series: C. D. WALcoTT. 
The paper described a new genus and two species 
of sponges found by Dr. A. C. Lawson in the lime- 
stone of the Steep Rock Series of Canada. 
The paper was discussed by A. P. Coleman. 
Evidence of Three Distinct Glacial Epochs in the 
San Juan Mountains of Colorado: WALLACE W. 
ATwoop and KirtLEy F. MATHER. 
Abundant evidence of two distinct Glacial 
epochs has been reported by several investigators 
from various mountain ranges in the western por- 
tion of the continent. During the past season 
glacial deposits have been examined and mapped 
about the margin of the San Juan Mountains, 
which deposits have been interpreted to indicate 
an epoch of glaciation distinct from the two later 
epochs that have been clearly recognized in the 
history of the range. 
For convenience, the three distinct epochs are 
referred to, beginning with the oldest as ‘‘San 
Juan,’’ ‘‘Big Horn’’ and ‘‘Uinta.’’ 
The composition, distribution and topographic 
relations of the San Juan glacial drift indicate 
that this earliest known epoch was separated from 
the Big Horn Glacial epoch by a much longer time 
than the Big Horn was separated from the Uinta. 
The two later epochs appear to have been sepa- 
rated by a much longer time than has elapsed since 
the last disappearance of glacial ice from the 
range. The San Juan Glacial epoch is so far re- 
moved from the present time that the glacial de- 
posits of that epoch are found at but a few places, 
where conditions were most favorable for their 
preservation. 
There are reasons for believing that the San 
Juan Glacial epoch may have been characterized 
by small ice caps among the western ranges rather 
than by Alpine glaciers, which were the prevailing 
type during the Big Horn and Uinta epochs. 
There are good reasons for believing that the 
San Juan epoch preeeded the development of the 
great canyons among the mountains, and, there- 
fore, that much of the sculpturing which has given 
form to the scenic features of the range is inter- 
and post-Glacial in origin. The time relation of 
the epochs of glaciation to other events in the 
physiographic history of the range were also 
suggested. 
The paper was discussed by H. H. Gregory. 
SCIENCE 
315 
Glacial Investigations in Minnesota in 1911: 
FRANK LEVERETT. 
A sheet of old caleareous drift deposited by an 
ice sheet radiating from central Canada covers 
nearly all of Minnesota and extends into western 
Wisconsin. The prominent moraines of western 
Minnesota, named by Upham, Itasca, Leaf Hills 
and Fergus Falls, were formed in the order named, 
as is shown by the glacial drainage from them. 
The rock constituents of these moraines show re- 
markable disintegration that suggests a possible 
pre-Wisconsin age. After these moraines were 
formed by the ice radiating from central Canada, 
there followed an ice movement radiating from the 
high tableland northeast of Rainy Lake. This 
moved across the northern ends of the above- 
named moraines and extended a few miles beyond 
the portion of the Mississippi above St. Paul. 
This produced the so-called ‘‘red drift.’? After 
this ice movement waned there followed a re- 
advance of the ice sheet radiating from central 
Canada which had its main axial movement through 
the Red-Minnesota-Des Moines Valley; but which 
also extended southeastward across the portion of 
the Mesabi Range west from Hibbing, Minnesota, 
and spread to the left and right in a basin which 
divides its drainage between the St. Louis and 
Mississippi Rivers. This ice movement deposited 
the so-called ‘‘gray drift’? of the Minnesota 
Reports. It forms only a thin veneer on the por- 
tions of the Leaf Hills and Fergus Falls moraines 
which it overrode, and it failed to cover all of the 
Leaf Hills moraine. The correlative position of 
the Lake Superior Lobe is found to have been but 
little beyond the western end of the present lake, 
in Carleton County, Minnesota. A large glacial 
drainage line opened a great valley along the St. 
Louis between Floodwood and Carleton, but was 
there turned southwestward because of the pres- 
ence of the Superior Lobe. The relations of this 
latest ice movement from central Canada to the 
Glacial Lake Agassiz are such as to make necessary 
a radically different interpretation from that 
given by Upham in his monograph on Lake 
Agassiz. 
The paper was discussed by Lawrence Martin 
and J. B. Tyrrell. 
Recent Studies of the Moraines of Ontario and 
Western New York: FRANK B. TAYLOR. 
The paper was entirely descriptive of moraines 
recently mapped in the areas of Ontario and 
western New York. 
Remarks were made by W. M. Davis and H. L. 
Fairchild. 
