REPORT OF THE DIRECTOR' I915 III 



The unsodded drift sand, as already stated, has Httle bonding- 

 power, ahhough in texture it may resemble the commercial' 

 material. 



The thickness of the molding sand layer ranges from a few 

 inches up to 4 or 5 feet, which represents about the maximum for 

 the thoroughly weathered layer. In the usual run of the bank the 

 thickness probably is not much more than 18 or 20 inches. Its 

 limits above and below are defined quite sharply, but less so in the 

 latter direction where it shows gradation rather quickly, that is, 

 within a few inches, into grayish open sand. The sod cover with the 

 soil usually amounts to 10 or 12 inches. 



The continuity of the layer shows no interruption as a rule from 

 minor irregularities of the surface; but the sand is cut off by 

 stream depressions and never extends far down the sides of steep 

 banks. The product comes mainly from the upland flats, 200 feet 

 or more above sea level. 



Composition and Textures 



The commercial molding sand consists almost wholly of quartz 

 grains bonded by clay. Examination of numerous samples evi- 

 dences its very simple mineral composition. Some unresolved 

 shale or sandstone, an occasional particle of feldspar, chlorite or 

 other silicate constitutes about the only variation that may be 

 noticed. The quartz particles, when freed from the attached coat- 

 ing of clay, are seen to be tinted a faint yellow by limonite which 

 adheres to their surface and lends the ochreous color to the sand 

 as seen in the mass. 



The ratio between granular aggregate and clay bond varies of 

 course in the bank within rather wide limits. In the usual run of 

 commercial sand of the finer sizes, the latter amounts to about one- 

 third or one-fourth by weight of the whole process. 



A feature of the sand that comes out prominently when viewed 

 under the microscope is the angularity of the individual particles, 

 even down to the very finest that can be seen. This is no doubt of 

 practical significance since it has been shown that angular particles 

 do not pack so closely as round ones and therefore should have 

 increased permeability to gases. The angularity is evidenced by 

 wedge-shaped forms and concave surfaces which are characteristic 

 of quartz sands comminuted by crushing under pressure rather 

 than by attrition or abrasion. Such sand is formed by glacial 

 erosion. The deposits of sand and clay in the Albany dis- 

 trict represent the finer residue of the load of rock debris v/hicli 



