MAGMATIC DIFFERENTIATION OF IGNEOUS ROCKS 647 
3. The coronation occurs in rocks not dynamometamorphosed, 
and accordingly, as has been pointed out by earlier investigators, 
it is no function of any orogenic pressure. 
4. The zones here treated I have observed in all of the very 
many microscopic thin sections that I have examined, of olivinifer- 
ous gabbros, norites, and anorthosites (with labradorite or still 
more basic plagioclase). In fact, the occurrence of the zones in 
these deep-seated rocks must be accepted as a general phenomenon. 
Fic. 48.—Photomicrograph (24:1) Fic. 49¢.—Drawing (24:1) 
Hyperitic-structured olivine-gabbro from Elverum, Norway. Consists of ca. 
65 per cent labradorite, 25 per cent diallage, 1o per cent olivine, traces of pyrite (in 
small cubes in the upper left portion of drawing). The labradorite laths show partial 
idiomorphism against the olivine (O].). Reactions rims between the olivine and the 
labradorite but not between the olivine and the diallage or between the labradorite 
and the diallage. 
5. The thickness of the zones increases in the deep-seated rocks, 
as a general rule, proportionately to the amount of An contained in 
the plagioclase. 
I cite: In the oliviniferous labradorite rock (Figs. 23-24) just 
mentioned (with Ab,An,) the total thickness of the zones regularly 
amounts to only 0.002 mm., sometimes to 0.005-0.010 mm., and 
exceptionally reaches 0.015 mm. In most olivine-hyperites (with 
plagioclase about Ab,An.), the thickness, as a general rule, is no- 
where less than o.06-o.08mm.; most frequently it amounts to 
