EPEIROGENIC MOVEMENT. 109 
ship of the successively formed shorelines of these and the other asso- 
ciated glacial lakes that this epeirogenic movement proceeded as a per- 
manent wave of land elevation from the periphery of the old ice-sheet 
inward to its central area.* 
Kperrrocenic MoVvEMENT CONTINUED TO THE PRESENT TIME 
The basin of Hudson bay, in the central part of the glaciated area of 
North America, is ascertained by Dr Robert Bell’s observations to be 
now slowly rising, mainly at the rate of a few feet in acentury ; but per- 
haps this uplift has ceased, as Mr J. B. Tyrrell thinks, in the vicinity of 
the mouths of the Nelson and Hayes rivers, on the southwest coast of 
the bay. On our Atlantic coast, from Boston to Cape Breton island, 
where the reélevation from the Champlain depression ranged upward 
to a maximum of about 300 feet in Maine, an ensuing subsidence of the 
land—that is, an epeirogenic movement of opposite direction—has lately 
taken place and is probably still very slowly in progress, its maximum 
amount near the head of the bay of Fundy being apparently at least 80 
feet. In southern Sweden the Champlain depression was succeeded 
during the retreat of the ice-sheet by reélevation of the land somewhat 
above its present height; next it was again depressed, but less than be- 
fore; and from this second depression it is now slowly rising at a maxi- 
mum rate of 2 or 3 feet in a hundred years. 
These notes of the continuance of the great Quaternary epeirogenic 
movements of the continental areas which suffered glaciation are pre- 
sented for the purpose of directing attention to their inconstancy, oscil- 
lations, and reversals. From the consideration of these well ascertained 
epeirogenic changes, it seems to me that the evidence of very slight tilt- 
ing of the Laurentian Lakes region now taking place, as made known by 
surveys of precise leveling which give comparisons between dates less 
than forty years apart, should notf be regarded as an important basis 
for predictions of changes of the course of drainage from these Lauren- 
tian lakes, turning their outflow away from the Niagara river to, the old 
glacial Chicago outlet 2,000 to 3,000 years hence. 
DuRaATIon oF NIAGARA FALLS AND THE POSTGLACIAL PERIOD 
e 
In our consideration of the time occupied by the Niagara river in the 
erosion of its gorge we find, as I think, ample reasons for distrusting the 
* Bull. Geol. Soe. Am., vol. ii, March, 1891, pp. 243-276; Journal of Geology, vol. ii, May-June, 1894, 
pp- 388-395; Am. Jour. Sci., iii, vol. xlix, Jan., 1895, pp. 1-18, with map; Am. Geologist, vol. xviii, 
Sept., 1896, pp. 169-178; The Glacial Lake Agassiz, Monograph xxy, U.S. Geol. Survey, 1896. 
+G. K. Gilbert: “Modification of the Great lakes by earth movement.’ National Geographic 
Magazine, vol. viii, Sept., 1897, pp. 233-247, with seven figures in the text. 
XVI—Butt. Grou. Soc. Am., Vou. 9, 1897 
