270 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Farther west on this gabbro belt, as for instance on King’s Creek, 
N. E. 4, See. 12, T. 49, R. 15 W., the rocks appear largely to belong to the 
olivine-bearing, orthoclase-free kinds, having at the same time a very basic 
feldspar. 
The red rocks that occur so largely associated with the gabbro of 
Duluth lie in it very irregularly, and form nothing like distinct belts, so 
far as I could make out. They may be seen in great patches, hundreds of 
feet square, and surrounded on all sides by the gabbro, and again, as at the 
quarry near Rice’s Point, in irregular veins from two to three inches to sev- 
eral feet in width. Much the most abundant kind of these red rocks is one 
which presents macroscopically a wholly crystalline texture, and a pinkish 
color mottled with green. Pink feldspar facets, now and then striated, 
quartz, and a greenish mineral may all be made out with the naked eye. 
Under the microscope the rock is seen to be chiefly composed of reddened 
orthoclase, but similarly reddened oligoclase, greenish hornblende, quartz 
and magnetite are also present. The quartz occurs both in quite large 
dominating plagioclase (labradorite), little orthoclase, some hornblende, diallage, magnetite, and 
titanic iron, and holds also very minute quantities of chalcopyrite and epidote, which is at times asso- 
ciated with quartz.” My study leads me to agree in the main with these conclusions. I take, how- 
ever, the hornblende to be wholly uralite, the plagioclase to be more often nearer oligoclase than 
labradorite, and the iron oxide ingredient to be wholly titaniferous magnetite rather than both mag- 
netite and titanic iron. The epidote, quartz, and chalcopyrite are so rare as not to deserve mention 
in any general description of the rock. The following analysis is given by Streng: 
SiQg .25 a2 22 Se.oed/b5 ssecise cass Sees owes se ew Sees cis sdeeisetemsaneweeeae sestecee 49.15 
ANS Os, o:- Sico:c aethrec Sheharya eres oeiee Seensee See ace etes oe tera 21.90 
Fe,03 Sees poesoss osteo ssseso cos SseeSoSss so scoebocshosesss cossenoncess 6. 60 
FeO «20258 d2iscjos det See ace cones eee oo eee ae Renee eee eee 4, 54 
OaO .52 5-2 aerccecis. sd acacteamban tes ener sasareeisa tt oer eee erce este ee ieerears 8. 22 
IS 0 eee eee eee Ker SON aS Sao coos eas ona seeesedatocediaccodcoes 3. 03 
KgO «.c2cosciratadiswiters cad Soe seca aoe tee ate etna en eiee mee eee eee renee 1. 61 
NasO) co ciceccisesce cc os cee basco cess cme t eneEmee snes tena meee eee eee 3. 83 
gO) 252 Sas cos oases esse wen cote anne ete winteeeelodSeseiseiocte <-idisoereae cece 1. 92 
100. 80 
PyO5. - ced own Jb cock tee Ses See cee ee ee er eee eters sisteadeceteleeteeaae 0. 33 
TiOg «65 scenns ssmeisc aden se ea eee sete ne CEE Oe ee eee eer ee eee ee ee 0. 18 
Winchell finds that the ‘‘ chief ingredients, which are always present, are plagioclase and pyrox- 
ene, but the latter is sometimes very small in amount.” He finds ‘‘also titaniferous iron, generally 
magnetic, almost always present, and sometimes in quantity sufficient to render it an iron ore of low 
grade, * * * Pyrite, caleite, epidote and chlorite also existin some parts, * * * especially as geodes, 
nests, and vein-fillings, or as products of change. The plagioclase ‘‘is provisionally taken for labrador- 
ite,” but in some places it is said to appear ‘‘more like anorthite.” The pyroxene is taken to be diallage, 
much of it ‘‘ fibrous from incipient change, the products being ferrite and viridite.” Hornblende and 
uralite are not mentioned. The iron oxide is considered to be titanic iron, although magnetic, because 
of the presence of the white decomposition product. 
