I/O The American Geologist. March, lso•^ 
est;"' but at the end of the Ice age the Adirondacks and the 
much larger region of the White and Green mountains, with 
probably the greater part of Maine, continued ice-covered 
after the glacial blockade was melted through along the 
Hudson-Champlain and St. Lawrence valleys, f Still later 
local glaciers, the last representatives of the departing ice- 
sheet, comparable with those of the English Lake District, 
existed in the Green and White mountains, forming in some- 
places admirable series of valley moraines accumulated by ice 
flowing northerly, in directions opposite to the earlier general 
glaciation.t 
Our mountains in the glacial drift area are less interesting 
than those of Great Britain as centers of drift dispersion, be- 
cause through the greater pr.rt of the Glacial period they 
shared in the general southward ice movement; but they have 
very significant later valley moraines, which, according to 
Agassiz, rival the recent recessional moraines of the Rhone 
glacier. A most inviting field for American glacialists is the 
m.ore thorough exploration and correlation of these last val- 
ley moraines of the White, Green and Adirondack moun- 
tains. 
SOME METHODS OF DETERMINING THE POSITIVE 
OR NEGATIVE CHARACTER OF MINERAL PLATES 
IN CONVERGING POL ARIZED LIGHT WITH 
THE PETROGRAPHICAL MICROSCOPE. 
By Dk. M.E. Wadswoeth, Houghton, Midi. 
For the elementary work in petrography in the A'lichigan 
College of Mines the laboratory is furnished with twenty-nine 
Bausch and Lomb petrographical microscopes specially made 
for the college, besides numerous other microscopes and 
petrographical apparatus, making it one of the best equipped 
laboratories known. 
*Appalachia, V (1889), 291-312 [also in the Am. Geologist, IV, Sept. 
and Oct., 1889]. 
tAm. Jour. Sci. (3), XLIX, I-18, with map, Jan., 1895 l'i'!-^<>> mcn-e fulK 
in Twenty-third An. Rep., Geol. Survey of Minnesota, for 1894]. 
JE. Hitchcock, Geology of Vt., I (1861), 82-87. L. Agassiz, Proc. 
A. A. A. S., XIX (1870), i6'i-i67 [also in Am. Naturalist, IV, 1870, and Ge- 
ology of N. H., Ill, 1878]. C. H. Hitchcock, Geology of N. H., 111,230- 
2qo. ' G. H. Stone, Am. Naturalist. XIV, 299-302, Apr'il, 1880. 
