EXPLANATION OF PLATES 657 



Explanation of Plates 

 Plate 43. — Types of Sand Grains 



Figure 1. — Glacial Sand from the Mer-de-Glace, Switzerland. (X 201/2.) 



Sharp, fresh, angular fragments, with but slight traces of 

 weathering and very little of wear. Composition various, poorly 

 assorted. Seen by reflected light. Collected by the author. 



Figure 2. — Sand washed from Wisconsin Till, Ypsilanti, Michigan. (X 201/..) 



Similar to figure 1, but showing evidence of both wear and 

 weathering. Apparently an admixture of glacial, aqueous, resid- 

 ual, and possibly seolian types. Reflected light. Collected by the 

 author. 



Figure 3. — Volcanic Sand of the angular Variety, shoiving no Erosion. 

 (X14.6.) 



Fragments glassy, vesicular, with flowage lines. Hawaii. Re- 

 ceived from Dr. G. P. Merrill, U. S. National Museum. Viewed 

 by transmitted and reflected light. 



Figure 4. — Volcanic Sand of the rounded Variety resulting from either Erosion 

 or a plastic Condition of the Material. ( X 14.6. ) 



Slaggy and glassy. Mount Pelee eruption of 1902. Collected 

 by Prof. T. A. Jaggar, Jr. Transmitted and reflected light. 



Figure 5. — Residual Sand from Diat)ase, Medford, Massachusetts. (X 14.6.) 



Granules angular and much weathered; rusted and more or 

 less opaque. Detached crystals near center. Signs of erosion 

 wanting. Supplied by U. S. Geological Survey. Reflected and 

 transmitted light. 



Figure 6. — Residual Sand from Diahase, Brighton, Massachusetts. (X 14.6.) 



Similar to figure 5, but of coarser texture. Supplied by Michi- 

 gan State Normal College. Reflected and transmitted light. 



