W. E. Hidden—Mineralogical Notes. 249 
gion, and again on the north side of Lake Superior, there must 
often arise great difficulty in separating the newer slates from 
the older schists. Such considerations do not, however, seem 
to me to take away anything from the arguments I have 
vanced in favor of the existence of a separation, for the nae 
from Lake Huron to southeastern Dakota, of the Archean for- 
mations into two distinct members. 
discordant members, to which for the present at least we 
should continue to give the classical names of Huronian and 
Laurentian. 
ArT. XXXIV.—Mineralogical Notes; by W. E. HIDDEN. 
Phenacite, a new locality. Rie Mr. J. G. Hiestand of Manitou 
Springs, Colorado o, I am indebted for a few specimens of 
quartz, topaz and sipemonsenie (microcline), on which J have 
found implanted, colorless crystals of ae a ie aap 
numbers. These specimens were discovered mer at 
bese oe El] Paso County, Colorado, about iui: tilted (by 
he road) from the locality previously announced by Messrs. 
Oseas and Hillebrand in this Journal. The phenacites are 
well polished and transparent, and are rig ee! highly 
modified. They vary in size from one to mm., are 
invariably lenticular in shape, with little or be prismatic 
evelopment and are implanted usually edgewise. A deter- 
mination of the specific gravity yielded 2-954, which is rather 
low considering the perfection of the crystals. Three different 
rhombohedrons, two scalenohedrons and three prisms were 
observed but their angles could not be determined with exact- 
ness with the means at hand. Later I shall endeavor to figure 
them and describe them more accurate 
y 
same ioealine where the Cant ane bastnesite were sect 
