282 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
convexity southward.” In central New York, since the Iroquois 
beaches in a direction less than three degrees south of east show a tilt 
rate of only 0.66 feet per mile, the direction of maximum tilt is appar- 
ently almost north and south. This suggests that the curve of the iso- 
bases continues eastward across New York State, and makes it seem 
probable that in New England the tilt would be greatest in a direction 
nearly due north and south, —surely only a few degrees east of north, 
and quite likely a few degrees west of north. 
DeGeer’s summary of the evidence of postglacial tilting in New Eng- 
land, in the form of raised marine beaches, benches, and _sea-floor 
sediments between Massachusetts and the Provinces, is the most com- 
prehensive and reliable study yet published. Incomplete as the evidence 
is, one cannot deny that there has been a postglacial uplift of the north 
with respect to the south. The discovery of further details, like that by 
FIGURE 3. 
Diagrams showing how postglacial tilting produces a discordance of altitudes among 
sand deltas. 
In the upper figure, three deltas stand at the same altitude, marking a horizontal water- 
plane which is controlled by the height of an outlet at the further end of the lake. In 
the lower figure this region has been tilted, so that the three deltas stand at different 
altitudes, marking a slanting water-plane. The deltas now stand higher than the 
outlet col. 
Tarr and Woodworth of the beaches at Cape Ann (Tarr), will doubt- 
less some day furnish the data for determining with more accuracy the 
true rate of tilt along the coast and the direction of the greatest slant. 
In the mean time, can we not gather valuable evidence of tilting by 
studying the water-planes of temporary ice-front lakes like the Sudbury, 
Nashua, and Charles ? 
To sum up: From the work of Taylor, Gilbert, Fairchild, and 
DeGeer, we might reasonably expect that whatever evidence came to 
light would show a tilt towards the south of a few feet to the mile, with 
its greatest slant in a direction about due north and south (considerably 
west of the N. 17° E. line of central New York). 
