102 F. Andrews—Glacial Markings of unusual forms. 
is represented ‘a section of certain marks produced in the same 
manner as those cuts of a stone planing engine where the tool 
trembles or vibrates in the grasp of the machine so as to cuta 
finely serrated groove. In. the specimens found the serrations 
were about one-quarter of a centimeter from crest to crest. It 
is possible that the regular vibrations thus recorded on the 
rocks had some fixed mathematical relation to the velocity of 
the ice, which might possibly be determined by calculation or 
experiment. 
New INDEX OF THE DIRECTION oF MOTION. 
Scoop Marks. 
These are singular phenomena and very difficult of explana 
tion. They are of two varieties, the striated and the unstria- 
. Fig. 5 is+a diagram intend 
to illustrate a typical form of the 
——— striated variety. The marks consist 
saceeialguiisliiialeiaamae till 
FBZ Sz wilt. They run nearly in the direc- 
ee eens iy 
: ra tion of the general striation of the 
= ——— flo had been inserted into 
== the rock and had cut out enoug 
of its substance to. make a sm 
and rather shallow concave channel. The end toward the 
east, or northeast from whence the drift action came, is abrupt, 
sharply-defined, and although the. angle of junction with 
