208 W. H. SHERZER 
Most of these were made at the southwestern end of a partially 
uncovered rock-basin, or trough, across which they cut in such a 
way as to show that the basin was already in existence when 
they were formed upon its distal side. The striz are shown in 
Fig. 6, emerging from the basin toward the right and diagram- 
matically in Fig. 7, upon the upper side, marked second move- 
Fic. 6.—Southwestern end of a rock-basin, Sibley quarry; partly filled with till 
and water. Two sets of striz are seen emerging from the basin; the set at the left 
being early Wisconsin, that toward the right pre-Wisconsin, probably Iowan. The 
basin itself is believed to have been formed by the Illinoian ice. In the background 
is seen the effect of the late Wisconsin upon the projecting ledge, with stoss phe- 
nomena toward the southeast. 
ment. An inspection of this diagram shows why they were not 
obliterated by the third, or early Wisconsin ice, being slightly 
in the lee of the western side of the basin. They are here 
intersected sufficiently, however, in order to settle the question 
of their relative age. Their position is such as to have rendered 
their removal probable by the late Wisconsin ice, but either its 
