410 The American Geologiet. June, i897 
they join again in Namekan lake, is some one hundred and 
twenty five square miles. And Namekan lake itself has two 
Outlets of about equal volume and less than half a mile apart, 
but in no way connected. Both streams flow over rock beds 
into Rainj'^ lake. 
The question of the origin of these lake basins need not 
be discussed here; it is sufficient to consider that, after the 
departure of the ice sheet, there were certain liasins (in drift, 
in rock, or in both) in each of which water accumulated un- 
til it overflowed the rim of the basin. In a few cases a basin 
had two points in its rim of the same altitude and lower than 
any other point, and thus a double outlet to the lake was 
formed. If one or both outlets flowed over drift deposits in 
all probability one of them would be of short duration : that 
there were formerly some such lakes is not improbable. How- 
ever, in the case of the lakes here described many, if not all, 
of the outlets flow over rock beds. The countrj' in which 
they lie is one where nearly all traces of weathered rock have 
been removed by glacial erosion, and the present rock surface 
is sound and unweathered and usually of the same character 
(as regards rock species, grain, hardness, etc.) at each of the 
outlets of any lake. Comparatively little sediment is brought 
into any of the lakes and practically all this small amount is 
deposited soon after its reception, so the water flowing from 
the lakes is almost entirely free from sediment and thus near- 
ly powerless to cut into hard rock. It ma}^ therefore be con- 
cluded that these lakes will be of comparatively long life and, 
moreover, that the possession of two outlets will be, unless the 
cause mentioned below operates, a feature of long duration. 
A possible cause for the brief duration of one outlet is to 
be found in difi:'erential elevation. It is well known that cer- 
tain portions of Minnesota have been elevated since the forma- 
tion of the beaches of the glacial lakes Agassiz and Warren, 
and, if the movement is still in progress,* some of the larger 
lakes here described will most probably loose one of their 
outlets in a comparatively short time. If northern elevation 
is still in progress the southern outlet of Lac la Croix; which 
is at present used only in high water, will become a normal 
* Cf. Robert Bell. "Evidences of northeasterly rising of the land 
along Bell river," BuH. Geol. See. Amer., vol. 8, pp. 211-250, pis. 23-24, 
Mch. 12, 1897. 
