. Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean . y 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 greatnumber of small, slender prisms of schorl grouped around a centralnucleus of two or more larger ones. The outline of the wholegroup is triangular, and the mass may be considered as forming onecrystal. All the interstices betwe
. Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean . y 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 greatnumber of small, slender prisms of schorl grouped around a centralnucleus of two or more larger ones. The outline of the wholegroup is triangular, and the mass may be considered as forming onecrystal. All the interstices between the prisms are filled by .trans-lucent quartz, and this mineral does not extend beyond the boundaryof the group. The whole is imbedded in feldspar. We may con-sider this to be the frame-work of a large crystal, which was notcompleted for want of a sufficient amount of bases to combine withcrystal of tourmaline. ^he siiicaj and ft is an instructive example of the incorporation ofextraneous matter within crystals. This is known to be the source of many conflicting results ofchemical analysis, and it is doubtless more common than is generally ANDALUSITE. Bemarkably fine specimens of this interesting mineral were obtained in the sands of theChowchillas Biver, at the point where it is crossed by the road, and in the upper stratum of thesedimentary deposits which rise in hills on each side of the stream. This stratum is a coarseconglomerate, and is charged with water-worn crystals of the mineral of various sizes. Thecrystals are also found imbedded in rounded masses of slate—the debris of outcrops higher upon the flanks of the Sierra. Some of the specimens found in the river did not appear to havebeen derived from the degradation of the conglomerate, and very probably have been transporteddirectly from the original source. The crystals tound in the bed of the stream were unusuallylarge, being from one-quarter to over an inch in diameter, and one to two inches long. Al
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