304 GEOLOGY. 
Ilmenite is a compound of titanic acid and sesquioxide of iron, in varying proportions; the 
analyses of specimens from various American and European localities showing the presence of 
from 8 to 53 per cent. of the former, and 46 to 91 of the latter. The mineral has not yet been 
made use of in the arts. It occurs in great beds in Canada, at St. Paul's Bay, and in crystals, 
similar to the Georgetown specimen, in the northern part of Sussex county, New Jersey, and in 
the adjoining town of Amity, Orange county, New York. Its occurrence in grains in the gold 
sand of California has also been noted by Professor Dana. 
TOURMALINE. 
Black tourmalines, or crystals of schorl, of immense size are found in the feldspathic veins on 
the north side of the Valley of San Felipe, San Diegocounty. Nearly all the crystals areimperfectly 
formed ; and the locality is chiefly interesting for their great size and peculiarities of aggrega- 
tion, which present some curious phenomena of crystallization. These phenomena will be: 
understood by inspection of the figure, which represents a great 
number of small, slender prisms of schorl grouped around a central 
nucleus of two or more larger ones. The outline of the whole 
group is triangular, and the mass may be considered as forming one 
crystal. All the interstices between the prisms are filled by trans- 
lucent quartz, and this mineral does not extend beyond the boundary 
of the group. The whole is imbedded in feldspar. We may con- 
sider this to be the frame-work of a large crystal, which was not 
SS SS completed for want of a sufficient amount of bases to combine with 
| CRYSTAL OF TOURMALINE. the silica, and it is an instructive example of the incorporation of 
extraneous matter within crystals. This is known to be the source of many conflicting results of 
chemical analysis, and it is doubtless more common than is generally supposed. 
ANDALUSITE. 
Remarkably fine specimens of this interesting mineral were obtained in the sands of the 
Chowchillas River, at the point where it is crossed by the road, and in the upper stratum of the 
sedimentary deposits which rise in hills on each side of the stream. This stratum is a coarse 
conglomerate, and is charged with water-worn crystals of the mineral of various sizes. The 
crystals are also found imbedded in rounded masses of slate—the debris of outcrops higher up 
on the flanks of the Sierra. Some of the specimens found in the river did not appear to have 
been derived from the degradation of the conglomerate, and very probably have been transported 
directly from the original source. The crystals tound in the bed of the stream were unusually 
large, being from one-quarter to over an inch in diameter, and one to two inches long. AB 
the edges and angles were rounded off and worn away in consequence of the constant attrition 
to which they had been subjected. Someof these crystals present a delicate pink, or rose color, 
shading into purple, and are translucent. 
This mineral occurs in granitic or metamorphic rocks, and is generally disseminated in long 
prisms in fine-grained mica slate. A mass of slate of this character, filled with Andalusite, 
was found on the bank of the river. Its color is dark; and it is very fine-grained, consisting 
chiefly of finely comminuted mica, mingled with clay. It is very compact, and has a silky or 
satin-like lustre. The crystals are much lighter in color, and, being harder than the slate, 
