24 Cincinnati Society of Natural History. 
7. Glaciers must descend slopes, and must be backed by large sup- 
plies of perennial snow. Icebergs act independently, and being water- 
borne, may work up slopes and on level surfaces. 
8. Glaciers striate the sides and bottoms of their ravines very un- 
equally,’acting with great force and effect only on those places where 
their weight impinges most heavily. Icebergs, on the contrary, being 
carried by constant currents, and over comparatively flat surfaces, 
must striate and grind more regularly over large areas, and with less 
reference to local inequalities of surface. 
9. The direction of the striz and grooves produced by glaciers de- 
pends on the direction of the valleys, That of icebergs, on the con- 
trary, depends upon the direction of marine currents, which is not 
determined by the outline of surface, but is influenced by the large 
and wide depressions of the sea bottom. 
10. When subsidence of the land is in progress, Py Es ice may 
carry bowlders from lower to higher levels. Glaciers can not do this 
under any circumstances, though in their progress they may leave 
blocks perched on the tops of peaks and ridges. 
He further said, that, in all these points of difference, the bowlder 
clay and drift of Canada, and other parts of North America, cor— 
respond rather with the action of floating ice than of land ice. 
More especially is this the case in the character of the striated sur- 
faces, the bedded distribution of the deposits, the transport of mate- 
rial up the natural slope, the presence of marine shells, and the 
mechanical and chemical character of the bowlder clay. 
He also enumerated the following Post-pliocene plants as occur- 
ring, in nodules, at Green’s Creek, and other places in Canada, to-wit: 
Drosera rotundifolia, Acer spicatum, Potentilla canadensis, Gaylus- 
saccia resinosa, Populus balsamifera, Thuja occidentalis, Potamo- 
geton perfoliatus, P. pusillus, Equisetum scirpoides. None of the 
plants are properly Arctic in their distribution, and the assemblage 
may be characterized as a selection from the present Canadian flora of 
some of the more hardy species having the most northern range. At 
Green’s Creek (near Ottawa) the plant-bearing nodules occur in the 
lower part of the Leda clay, which contains a few bowlders, and is 
apparently, in places, overlaid by large bowlders, while no distinct 
bowlder clay underlies it. The circumstances which accumulated the 
thick bed of bowlder clay near Montreal, were probably absent in the 
Ottawa valley. In any case, we must regard the deposits of Green’s 
Creek as coeval with the Leda clay of Montreal, and with the period 
