BRIDGING THE AGES OF ICE 
- 357 
Now, if the phenomena are coincident, as is forcibly suggested, 
it follows that, as has already been urged by Chamberlin,^^ this 
moraine was formed, not during an independent ice-period, but 
during a temporary halt and slight re-advance of the slowly re¬ 
treating ice-sheet which formed the drift without its limits. 
^Tncidentally the observations herein recorded indicate (1) from 
the essentially homogeneous and unquestionably unipartite charac¬ 
ter of the drift-sheet above the loess, especially in section 6, that 
the Torrellian hypothesis of the deposit of a ground-moraine and a 
superficial moraine by each glacier is invalid; and (2) from the 
disappearance of the blue coloration downward in sections 6, 8 
and 10, that this blue color is not normal and changed to brown 
or yellow by oxidation from above, as urged by Hawes,Julien,^® 
Von den Broek,^^ Shaler,^® and others, but is in some way ac¬ 
quired.’’ 
The Capitol Hill till sections in Des Moines, now form one of 
the notable Glacial localities in America. During the past thirty 
years this place and the vicinity receives the repeated visits of 
many of the most eminent scientists of the world. It so happens 
that the two thick drift-sheets which cover Capitol Hill are the 
youngest and oldest but one of a succession of five great glacial 
mantles, the intermediary sheets being absent. Now, the stone 
bridge, of which a view is given in the accompanying plate, joins 
two unrivaled sections, on opposite sides of the Court Avenue 
speedway. The south abutment rests on the most ancient drift 
sheet and the deposits beneath; while the north end of the span 
abuts the most recent drift deposit. 
The arch not only spans a fine boulevard but it connects the 
two glacier dropped beds which in point of time were separated 
by thousands upon thousands of years. Geologically this noble 
structure spans, as it were, the Glacial Period as does the rainbow 
the heavens. It is fitting that a majestic monument should mark 
the positions of the famous McGee drift sections, which first gave 
definite clue to the grand conception of a multiple Ice Age. It 
11 Geology of Wisconsin, 1873-1877, Vol. II, pp. 214-218, 1877. 
_ 12 Geology of New Hampshire, Vol. Ill, p. 333, 1878. 
13 Proc. American Assoc. Adv. Sci., Vol. XXVII, p. 352, 1879. 
14 Mem. sur les Phenomenes d’Alteration des Depots superficiels par I’infiltration 
des eaux Meteoriques, pp. 147-168, 1881. 
15 Glaciers, p. 165, 1881. 
