602 



WincJiell and Miller- 



as to indicate that it is a condition of long standing. The 

 feldspar shows no twinning and much of it is probably 

 orthoclase, but other feldspars are not excluded. Calcite, 

 hornblende, mica, etc., are present in very small amount. 

 Magnetite particles were discovered by using a magnet. 



In addition to the minerals and organic material, this 

 snow dust contains a considerable number of diatoms, 

 one of which is shown in the photomicrograph (fig. 2). 

 There seems to be more than one kind of diatom present, 

 and the sizes vary, but the usual size in this dust is 0-006 

 to 0-01 mm. in width and 0-02 to 0-035 mm. in length. They 

 are roughly cigar-shaped and so small that it would 

 require 750 laid end to end to measure one inch, and more 

 than three billions to fill one cubic inch. The portion of 

 the diatom found in the dust is the test, which is composed 

 of hydrous silica, or opal, and has various very regular 

 markings over its surface. 



Microscopic measurements of the size of the dust par- 

 ticles show that they range from about 0-003 mm. to about 

 0-1 mm., but a surprisingly large percentage falls within 

 much narrower limits, namely 0-008 to 0-025 mm. 



At our request, a mechanical analysis of the material 

 was made by Professor H. W. Stewart of the Soils 

 Department of the University of Wisconsin. He reports 

 that the water-free weight of the sample used was 1-8268 

 grams, and that it yielded the following : 



;es. Size. 



Clay Less than -005 mm. 



Fine silt -005 to -010 



Medium silt -010 to -025 



Coarse silt -025 to -050 



Very fine sand -05 to -10 



Fine sand -10 to -25 



Medium sand -25 to -50 



Coarse sand -50 to 100 



Fine gravel 1-00 to 2-00 



Total 



Weight 





Grams. 



Per cent. 



0-2046 



11145 



04020 



22005 



10261 



56-169 



01094 



5-988 



00222 



1-215 



0-0189 



1035 



00106 



0-580 



0-0053 



0-290 



0-0197 



1-078 



1-8188 



99-504 



Professor Stewart reports also that the organic con- 

 stituents were allowed to distribute themselves wherever 

 they would among the separates, with the result that 



