1 54 PROCEEDINGS OF THE ALBANY MEETING 



Ferrous oxide seems to be a universal constituent of dolomite. The sedimen- 

 tary calcite of Mississippi Valley limestone, tested by the writer, showed no 

 ferrous oxide. From their ferrous oxide content it is certain that dolomites 

 were formed under reducing conditions. The absence of ferrous oxide in the 

 primary calcite of limestones suggests a difference in the chemical conditions 

 of limestones and dolomite deposition. 



The wi'iter succeeded in differentiating calcite from dolomite with a modified 

 form of the standard Lemberg solution, consisting of 4 grams of fresh AlCl;; 

 crystals, 6 grams extract of logwood, and 1,400 grams of water, boiled for 20 

 minutes with constant stirring and then filtered. Due to its ferrous oxide 

 content, dolomite turns blue in a dilute HCl solution containing a few drops of 

 freshly prepared potassium ferricyanide. Sedimentary calcite was unaffected 

 by this solution, but most vein calcite turned blue. 



Presented in abstract extemporaneously. 



SOME FURTHER CONSIDERATION OF THE FORCES DEVELOPED IN CRYSTAL 



GROWTH 



BY ARTHUK L. DAY 



Presented in abstract extemporaneously. 



PROBLEM OF THE ANORTHOSITES 

 EY N. L. BO WEN ^ 



(Abstract) 



By reason of their occurrence almost exclusively in the ancient terranes, of 

 their great size, and of their comparative uniformitj^ of composition over wide 

 areas, the anorthosites present a number of problems to the petrologist. But 

 it is perhaps more in virtue of their simple composition that the anorthosites 

 may be said to present a special problem. Normally, rocks are made up of 

 several minerals, and when considering their magmas we have come to regard 

 the various minerals as existing therein in mutual solution. Thus, though 

 minerals as individuals are often among our most refractory materials, 

 magmatic temperatures, or the temperatures of mutual solution, are believed 

 to be, and for very good reasons, comparatively moderate. What, then, of 

 the solution theory as applied to anorthosites which, typically, consist almost 

 exclusively of the single mineral plagioclase? Were they ever hot enough to be 

 molten per se? Chemical considerations and field facts both indicate that this 

 latter question is probably to be answered in the negative. The chemical con- 

 siderations bring out the improbability of the formation of anorthosite in any 

 manner other than by the accumulation of plagioclase crystals precipitated 

 from solution in a mixed magma, and therefore the probability that anor- 

 thosites were never molten as such. The field relations of the anorthosites, as 

 recorded by numerous observers, seem to be entirely consistent with this view 

 of their origin. 



An examination of the anorthosites of the Adirondack area and of the Morin 

 area with this aspect of the question especially in mind has strengthened the 



