Boston Meeting of the Geological Society. 223 
sisting of till on their surface, and mainly to depths of five to ten feet 
or more, while stratified sand or gravel form their nucleal and greater 
part. The till is believed to have been englacial, being thence depos- 
ited, like a veneer, on unusual subglncial stream accumulations of mod- 
ified drift. (This paper will be presented in full in a later number of 
the American Geologist.) 
57. Diversity of the glacial drift along its boundary. Warren 
Upham. (Read by title.) Different phases of the drift near its limits 
across the United States and about the Wisconsin driftless area were 
considered in relation to the methods of transportation and deposition, 
ensuing erosion, and sequence in age. Remarking how nearly coinci- 
dent the earlier and later drift boundaries are for the long distance 
from the Scioto river in Ohio eastward to the Atlantic coast, the author 
thinks that they cannot be referred to distinct epochs of glaciation sep- 
arated by a long interglacial time, as some have supposed, when the ice- 
sheet made a long retreat to the north or was wholly melted as now 
from this continent. He believes it more reasonable to appeal instead, 
as Prof. James D. Dana has recently done (Am. Jour, of Science, Nov., 
1893), to meteorological differences between the Mississippi basin and 
the eastern states, whereby comparatively long glacial retreats and re- 
advances could take place at the west while in the east the ice-border 
more steadily remained near the drift boundary. 
In New Jersey the manner of transportation and deposition of the 
early extra-moraine drift is held to be a probable explanation of its un- 
even distribution, occurring near its limits in patches which have led 
Prof. R. D. Salisbury to suppose that a long time of denudation inter- 
vened between the times of deposition of the early and the late drift. 
The early accumulation and advance of the ice to its extreme limits 
gave a comparatively thin ice-sheet with feeble erosive action on much 
of the outer part of the drift-bearing area. Its drift there was nearly 
all brought from considerable distances at the north and was deposited 
in obedience to the currents of the marginal portion of the ice-sheet. 
Now we have upon many districts of the thick later drift the very re- 
markable aggregations of the till called drumlins, which appear to have 
been amassed by convergent currents of the ice-sheet during its retreat 
(Am. Geologist, Dec, 1892). Similar selective action of the outflowing 
early ice advance close to its farthest limits is thought by the author to 
have amassed that outermost early till in the patches where it is now 
found, having received little change by later erosion. 
The well oxidized and leached condition of the early outer drift 
everywhere is easily referred to its derivation chiefly from the preglacial 
residuary clays, decaying rocks, weathered rock cliffs and tors, and 
boulders of secular disintegration. Its smoothed surface, without the 
inequalities of accumulation which provide basins for the myriad lakes 
and lakelets of the later drift, seems attributable to the gentle currents 
of the early thin ice-sheet, in contrast with which the later thick ice 
powerfully eroded its rock bed, even close to the boundary, and tumul- 
tously heaped or very irregularly spread its drift with many lake- 
enclosing hollows. 
58. Notes on the microscopic structure of siliceous oolite. E. O. 
Hovey, New York City. In the Am. Jour, of Science for Sept., 1890, a 
siliceous oolite from near State College, Center county, Pennsylvania, 
was described by Dr. E. H. Barbour and figures were given. That 
author did not use polarized light in investigating the rock. Some of 
the same material came into the present writer's hands, and, having 
been studied between crossed nicols, the details of structure were clear- 
ly brought out and were described at length. The spherules, which are- 
very uniform in size and rather evenly distributed through the rock, 
consist of two distinct zones of minutely fibrous chalcedony deposited 
about aggregates of very fine-grained quartz sand or fragments of quartz . 
