Age of the St. Croix Dalles — Upham. 35 s 
largest about 25 feet in diameter, and the deepest exceed- 
ing 80 feet in depth, occur most abundantly near the steam- 
boat landing of Taylor's Falls, at the central part of the 
Upper Dalles, and within a distance of fifty rods north- 
ward. They are unsurpassed by any other known locality, 
not even excepting the Glacier Garden of Lucerne, in re- 
spect to their variety of forms and grouping, their great 
number, the extraordinary irregularity of contour of the 
much jointed diabase in which they are eroded, and the 
difficulty of explanation of the conditions of their origin. 
If it be desirable to suggest a probable measure in 
years for the ages of the gorge and the giants' kettles at 
the St. Croix Dalles, I would venture to estimate the whole 
duration of the Ice age as about 100,000 years, of which 
about half, or 50,000 years, would probably belong to the 
early or Kansan glaciatioji ; about 15,000 years, according 
to Winchell, would measure the Buchanan interglacial 
stage in Minnesota; perhaps 30,000 years may be allotted 
to the later Illinoian and lowan glaciation ; and the de- 
parture of the ice-sheet, in its moraine-forming Wisconsin 
stage, occupied probably about 5.000 years. Under these 
estimates, the rock gorge here would be about 40,000 
years old, its last 5,000 years being approximately the time 
since the latest parts of our continental ice-sheet were 
melted away. For the giants' kettles, about 7,000 or 8,000 
years, as I think, may be assigned as their age, being nearly 
the same as that of the beginning of erosion of the gorge 
of the Mississippi river between Fort Snelling and Minne- 
apolis. 
