60 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, 1 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 



Glacial Geology of the Schenectady Quadrangle. N. Y. State Mus. Bui. 154. P- 24 and 25. 



