114 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
present in all sections examined. It is a curious fact that, although it has 
been found affecting the outer borders of the plagioclases, these are for the 
most part free from the quartz saturation. In many cases it is evident from 
the existence of a regularly outlined core without quartz within the feldspar 
crystal, and of an outer border, of greater or less width, saturated with 
quartz, that the replacing process has gone on from without, inwards. In 
other cases, again, the feldspar crystals have plainly been more or less 
shattered into fragments, and cracked across, before the deposition of the 
quartz. 
In those kinds which macroscopically are especially granite-like, show- 
ing large feldspar and quartz areas one-twentieth to one-fifth inch across, 
the larger quartz areas appear much like the quartz of true granite, 
filling, as in granite, the spaces between the feldspars. But the same 
sections sometimes show the saturating, club-shaped, secondary quartz along 
with these larger interstitial quartz areas, and then the larger areas often 
polarize together with a number of the smaller, undoubtedly secondary 
ones in the immediate vicinity, in which case all must be taken as secondary. 
In some sections of these coarser rocks, however, none of the plainly 
secondary saturating quartz is found in the feldspars, and then it cannot be 
shown that the coarse quartz is not an original ingredient. In the figures 
of Plates XIV and XV, I have attempted to illustrate the occurrence of the 
secondary quartz of these rocks. Figs. 1 and 4 of Plate V, and Figs. 13, 
14, 15, 16 of Plate XIII, showing secondary quartz as characterizing the 
already described orthoclase-gabbros and felsitic porphyries, should be 
referred to for comparison. 
About two-thirds of the sections show sparsely scattered augite crys- 
tals, which present the same peculiar red and brown to black ferritic altera- 
tion that characterizes the augites of the felsitic porphyries, as above de- 
scribed. The unaltered augite is commonly present only in cores. A very 
few sections show, instead of the augite, a fibrous green hornblende, whose 
uralitic nature is extremely probable. Titanic iron or magnetite occurs in 
two or three sections. 
A perusal of the following tabulation of observations on these rocks 
will serve to make it plain that they present a tendency to graduate in four 
