254 J. D. TRUEMAN 
The recent article by Scherzer’ on the recognition of the types 
of sand grains is interesting in this connection. Scherzer considers 
that well-rounded grains are typical of eolian deposits. In this 
paper reference is made to the experiments of Daubrée which seemed 
to show that granules less than o.1 mm. in diameter? cannot be 
rounded by water action. Typically rounded grains of zircon were 
observed by the writer in the section of zircons illustrated in Fig. 9 
under .o6 mm. in diameter. 
Fic. 8.—Zircons from Butte granite. X40 
The writer’s tests indicate that the zircons of granitic rocks 
have generally good crystal form, sometimes with perfect faces as 
shown in Fig. 8 and in other cases having somewhat rounded out- 
lines. The zircons represented in Fig. 8 are, by the way, from a 
biotite granite and form an exception to the rule proposed by Derby 
with regard to the relative perfection of form between the amphibo- 
litic and micaceous types. Tests made on about 15 specimens of 
«W.H. Sherzer, Bull. Geol. Soc. Amer., XXI (1919), 625-62. 
2 V. Ziegler in an article which has just appeared states that it is improbable that 
grains less than 0.75 mm. in diameter could be well rounded under water (Jour. Geol., 
XIX [1911], 654). 
