214 The American Geologist. October, 1900 
Chapter IV. Plagioclasyte. 
The term "plagioclasyte" recently proposed by the French 
Commission on rock nomenclature, is intended to supplant the 
older name "anorthosyte" which has been the cause of so 
much confusion in petrographic literature. The latter term 
has obtained much currency in American geological literature 
especially through the writings of Hunt, ^dams, Lawson, and 
Coleman, but it is open to serious objection, since it has been 
confused not only with anorthite, but also with anorthoclase.* 
Plagioclasytes, which occur not only in large masses in 
Minnesota, but also in Canada, New York, Norway, Finland 
and other countries, constitute a petrographic type of distinct 
individuality, not a local freak of nature, but a normal rock 
type, which is found in unvarying composition, in mountain 
masses, and in widely separated areas. 
The plagioclasytes of Minnesota have received various 
names from the geologists who have made them a study. J. 
G. Norwood f was probably the first to definitely identify them, 
and he simply termed them "feldspar rocks." Hunt,;]; studying 
the same rock in Canada a few years later, called it "labra- 
dorite rock" from its composition, or "noryte," since it was 
supposed to be the equivalent of the original noryte from 
Esmark, Norway. At the same time he proposed to call the 
formation "Norian," from his new name of the rock largely 
composing it, since he considered it of sedimentary origin. 
Irving,§from very questionable determinations of the feldspar, 
called it "anorthite rock." Finally Lawson || suggested the 
term "Carltonian" to designate the plagioclasytes as a forma- 
tion, which he separated^ sharply from the other gabbros of 
northeastern Minnesota. 
*In the French language the triclinic soda-potash feldspar is called 
"anorthose," with which the rock name is inevitably often confused. 
tReport of a Geological Survey of Wisconsin, Iowa, and Minnesota: 
D. D. Owen. Philadelphia, 1852, p. 380. 
JAmer. Jour. Sci., Nov. 1869. 
§R. D. Irving, Geology of Wisconsin, III, 1880. 
!1A. C. Lawson: Anorthosvtes of the Minnesota Coast of Lake Superi- 
or, Geol. Nat. Hist. Surv. Minn. Bull. No. 8, p. 23. 
^Winchell, Van Hise, and Elftman have shown that the separation 
cannot be maintained; the rocks grade insensibly one into the other. 
