The Dustfall of March 9, 1918. 609 



moist areas which are covered by vegetation. This is a 

 type of erosion which may carry material ■ i up hill ' ' from 

 a dry region of little elevation to a moist region of greater 

 elevation. In the case here presented however, the 

 material probably came from a mountainous arid region 

 to an area of lower elevation. 



The soil of any region is probably derived in consider- 

 able part from material transported by the wind. 



Diatoms and all sorts of plant and animal life of 

 microscopic size as well as fragments of larger organisms 

 may be transported long distances by the wind. 



Dr. Albert Mann, Plant Morphologist of the U. S. 

 Department of Agriculture, has examined these diatoms 

 and reports that they belong for the most part to the 

 species Nitzschia amphioxys (Ehr) W. S. and Navicula 

 borealis Ehr, the former being a little more abundant 

 than the latter, and being represented exclusively by a 

 particularly minute variety. Diatoms are algae and grow 

 only in water, but these two species are doubtless peculiar 

 to localities where there is only the thin film of water 

 which is brought up by surface tension in sphagnum bogs 

 and present in damp moss on the trunks of trees, since 

 their extreme minuteness enables them to live and 

 multiply in such thin films of water. 



Madison, Wisconsin. 



