688 W. H. SHERZER RECOGNITION OF TYPES OF SAND GRAINS 



subdivisions (page 152) — regular, acicular, irregular, and absent. The 

 first division comprised the ordinary crystalline inclusions, such as chlo- 

 rite, mica, rutile, apatite, garnet, zircon, magnetite, etcetera, which might 

 occur in various combinations or under exceptional forms. The acicular 

 division included those grains showing tufted, sheaf-like or other combi- 

 nations of fine needle-like inclusions, some of which were identified as 

 sillimanite. Under "irregular inclusions'^ are referred the gas or liquid 

 inclusions, with or without bubbles. The author's study of the crystal- 

 line rocks of his region convinced him "that acicular and irregular in- 

 clusions preeminently abound in the quartz of granite; that the regular 

 group is to be found in various proportions, but always in relatively 

 larger numbers in the quartz of gneiss and the younger schistose rocks" 

 (page 154). In tracing the sands to the parent bed on the basis of the 

 quartz inclusions, confirmatory evidence could often be obtained from 

 the inclusions or certain peculiarities of the associated feldspar or other 

 minerals. In summarizing his success in applying the method, Mackie 

 says : "Several groups have been identified with all but absolute certainty. 

 Eegarding others, which may be traced to more than one locality, there 

 is, of course, at times some doubt, while regarding a considerable re- 

 siduum I have not yet even a hint to go by in the matter of their identi- 

 fication" (page 158). This work and the method employed suggests 

 many problems awaiting solution in all sections of the country. An at- 

 tempt to utilize the method in tracing the origin of the Sylvania sand is 

 given toward the close of this paper. 



^OLiAN Sand Types 



Sands of any of the previously described types — -glacial, volcanic, re- 

 sidual, and aqueous — may come within the grasp of the winds, and suffer 

 still further abrasion under the infiuence of this new agency. In com- 

 parison with the water, the granules in air strike with so nearly their full 

 weight that the shaping of such grains is much more rapid and complete. 

 Applying the formula previously referred to, Mackie^^ calculated th^t 

 with a current velocity of 2 miles an hour and a wind velocity of 8 miles 

 an hour, the rounding effect of the wind on quartz grains is about twenty- 

 nine times greater than is that of the water, and that particles less than 

 one-fifth the diameter of those rounded by water will be rounded to an 

 equal extent by the wind. The factors involved in this rounding process 



23 Mackie : On the laws that govern the rounding of particles of sand, p. 310. bee 

 also 



Udden : Erosion, transportation, and sedimentation performed by the atmosphere. 

 Journal of Geology, vol. ii, 1894, p. 318. 



