Brief Notices. 233 
coasts. The fields in Manitoba and Southern Saskatchewan supply 
lignitic coal well adapted for domestic use. The extensive coal- 
fields of Alberta, containing coals of a wide range of character, form 
Canada’s greatest coal reserve. The interior of British Columbia 
contains many coal areas. 
6. Tue Position oF THE VIBRATION PLANE OF THE PoLARISER IN THE 
PxrrograpHic Microscopr. By F. E. Wricar. Journ. Washing- 
ton Acad. Sci., v, pp. 641-4, 1915. 
N petrographic microscopes with fixed polarizers the plane of the 
transmitted light is parallel to either the vertical or the horizontal 
spider-line of the eye-piece. The better position is that in which 
most light is transmitted. The light from the sky is always partially 
polarized, the amount varying with the distance from the sun’s 
position, and further effect is produced by the reflection at the sub- 
stage mirror. ‘he second factor was found to be negligible. The 
first, however, is important, and to obtain the best illumination the 
observer should set the plane of the polarizer parallel to the vertical 
spider-line in the early morning and late afternoon, and at right 
angles thereto at midday, but, since the intensity at midday is so 
much greater than when the sun is low, the better position for a fixed 
polarizer is for the plane to be parallel to the vertical spider-line of 
the eye-piece. 
7. A Surprz Device ror tat GrapuicaL SoLvrion oF THE Equation 
A=8.C: a Guotoeicat Prorracror. By F. E. Wricur. Journ. 
Washington Acad. Sci., vi, pp. 1-7, 1916. 
Y the use of reciprocals the variables may always be taken as less 
than unity. Rectangular co-ordinates, together with an arm 
revolving about the origin, are used in conjunction with squared 
paper, the scales being varied to suit the particular equation. The 
geological protractor is a particular form: from it the apparent dip 
of a bed can be read off directly for any angle of dip of stratum and 
for any azimuth of vertical section. 
8. THe CorreLation oF Porasstum AnD Maenestum, Soprum anv Iron, 
In lenxous Rocks. By Henry S. Wasnineton. Proc. Nat. Acad. 
Sci., i, pp. 574-8, 1915. 
fJVHE correlation of the elements has not yet received much study 
except the relation based upon silicity. It appears that in 
igneous magmas potassium and magnesium, and sodium and iron, 
tend to vary together, the evidence being of two kinds—petrological 
and mineralogical. 
9. PREssuRE as A Factor in THE Formation oF Rocks anp MINERALS. 
By Joun Jounstoy. Journal of Geology, xxiii, pp. 730-47, 1915. 
ENERALLY the so-called physical changes (e.g. the melting- 
point of a pure substance) has been overestimated as compared 
with the influence of pressure on chemical changes. Change of 
effective pressure will in general alter the configuration of the 
various fields of stability in a system, but the effect will not be 
marked unless the concentration of one of the components changes 
appreciably with the change of pressure. In any discussion of the 
