SPIIERULITIC CRYSTALLIZATION. 
449 
1888, Mr. J. J. Harris Teall says, on page 402: “ The spher- 
nlites in many of the acid rocks probably answer in compo¬ 
sition to micropegmatite. * * * The present writer is 
inclined to regard these spherulites as due to the simultane¬ 
ous crystallization of quartz and feldspar. * * * If this 
be correct, then the spherulites in question are simply special 
modifications of the pseudospherulites and micropegmatite.” 
To which might have been appended a foot-note similar to 
that numbered (2) on page 338 of the same memoir. Brog- 
ger has expressed the same view in his great work on the 
minerals of the syenite-pegmatite dikes of Southern Norway.* 
He considers microfelsite a submicroscopic intergrowth of 
orthoclase and quartz, basing his argument on the optical 
and chemical characters of microfelsitic spherulites, and 
states that if one approaches the subject from a study of the 
pseudospherulites of granophyre the conviction is more 
quickly reached that microfelsite is the crystallitic equiva¬ 
lent of granophyric pseudospherulites; and it is not difficult 
to find all transitions between the two in the proper thin 
sections. 
In the articles on Obsidian Cliff by the present writer the 
term microfelsite was not used, as there seemed to be no 
occasion for introducing this ambiguous term into the descrip¬ 
tion of a rock whose manifold microstructures could be ex¬ 
plained without it. The minutest spherulites appeared to 
be nothing more than very small forms of larger ones, whose 
structure and composition could be observed, and they were 
so considered. 
It may seem that after the definite statements already 
quoted as to the transition of microspherulites to micropeg¬ 
matite or granophyric intergrowths it would be unnecessary 
to pursue the subject further; but there remains sufficient 
uncertainty regarding the exact nature of these microscopic 
crystallizations to warrant a careful investigation of them 
* Brogger (W. C.). Die Mineralien der Syenitpegmatit-gange, etc., being 
Zeitschrift fur Kryst. u. Min. von P. Groth. 8°. Bonn, 1890, vol. 16, pp. 
552-553. 
