69 NEW YORK STATE MUSEUM 
them into the lake when they were laid down in more or less sorted 
and stratified deposits. The deltas of the Mohawk and other large 
tributary streams of that period furnish the principal supplies of 
the molding sand. 
The typical product of this region, that is the finer grades, is 
characterized by a degree of comminution and angularity of the 
particles unusual to water-worn sands. It is probable that these 
features are the result of ice erosion in the first place, but they 
may have been further developed by wind action after the retreat 
of the waters and before the deposits became fixed in place by 
vegetation. At least there are indications in places that the winds 
effected the final sorting and have deposited the sands in their pres- 
ent attitude which is quite different from that resulting from water 
work. 
The molding sand does not mark the outcrop of any definite layer 
or layers within the series of interstratified clays and sands, but 
forms a mantle that follows the surface configuration. It rises and 
falls with the minor irregularities of the surface, showing a variation 
of elevation inconsistent with the regular order that would be 
expected from a water-laid deposit. The thickness of the molding 
sand is also quite variable, running from a few inches in some places 
to several feet in other localities. These features have recently 
been remarked by Stoller,‘ who bases on them a theory as to the 
secondary origin of the molding sand through the operation of 
surface agencies, specially oxidation and moisture. “It appears 
to be a necessary inference from this that surface conditions are 
a determining cause in the origin of the layer of molding sands. 
In dry seasons of the year when the surface soil has been largely 
deprived of water by evaporation, an upward movement of the 
ground water by capillarity takes place. If the ascending ground 
water carries iron in solution, the iron may be oxidized and pre- 
-cipitated as it approaches the surface. In this way, the film of iron 
oxid coating the particles of sand is formed. The porosity of 
sand, admitting air to a considerable depth below the surface and 
at the same time favoring evaporation, facilitates the process. In 
addition to the iron, it is probable that small particles of clay are 
carried upward by the moving ground waters and are fixed through 
cementation by the iron oxid. These processes continue from 
season to season through a long period of years, the layers of 
molding sand being periodically added to at the bottom until it 
1 Gla-ial Geology of the Schenectady Quadrangk. N.Y. State Mus. Bul. 154, p. 24 and 25. 
