354 The American Geologist. Dec-iiiber, 189;? 
regions on each side.* Siiuihtrly in England, accoiding to tlic 
observations of Mr. G. W. Lamplugh, a contluont ice-sheet flow- 
ing from Scandinavia and Scotland was i)nslied np on the York- 
shire coast, bringing ninch englacial drift, with marine shells, 
which it had eroded and gathered np from the shallow and almost 
level basin occnpied l)efore the Ice age and again afterward by 
the North sea.t 
The manner in which the ice gathered drift into its basal por- 
tion from any plain tract seems to me explainable by a consid- 
eration of the currents of outtlow toward its border. In the cen- 
tral area of the ice-sheet the currents of its upper and lower por- 
tions probably moved outward with nearly e(iual rates, the upper 
movement being slightly faster than at the base. Ui)on a belt 
extending many miles back from the margin, however, where the 
slope of the ice-surface had more descent, the upper currents of 
the ice, unsupported on the outer side, would move mucii faster 
than its lower currents which were impeded b}' friction on the 
land. There would he accordingly within this belt a strong 
tendency of the ice to flow outward with somewhat curved cur- 
rents, tending first to carry the onwardly moving drift gradually 
upward into the ice-sheet, and later to bear it downward and de- 
posit it partly beneath the edge of the ice and partly along the 
ice boundary. 
Ahlafioii caashi<i Englacial Drift to hecniiic tSiii>rr(//(irl(iI. — - 
Whenever the warm climate terminating the Griacial period ex- 
tended unchecked through many years, the depth of the ablation 
(H- superficial melting of the outer part of the ice-sheet was 
probably not less than 15 to 25 feet each summer, as has l)een ol)- 
served on the Muir glacier in AlaskaJ and on the Mer de Grlace in 
Switzerland. ? At such rates of melting any district enveloped 
by ice 2,000 to 4,000 feet thick, as was true of the central por- 
tions of New England and doubtless also of a l)road belt thence 
west to the Laurentian lakes and to Minnesota and southern 
*(Teol. and Nat. Hist. Survey of Minnesota, Ninth Annual Report, 
for 1880, pp. 322-326 ; Final Report, vol. r, 1884, pp. 603, 604. Geol. and 
Nat. Hist. Survey of Canada, Annual Report, new series, vol. iv, for 
1888-89, pp. 38-40 E. 
tQuart. Jour. Geol. Society, London, vol. xi.vri, ISHl, pp. 384-431, 
with maps and sections. 
iH. F. Reid, in National <Teopraphic Maj^azine, vol. iv, pp. 31. 38. 
.March, 1892. 
§Prestwich's (ieology, vo]. i, p. 176. 
