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The abrupt hillocks thus composed, as well as the highly inclined folia of the common varieties of gneiss, strike N.N.E. or a little more easterly, and S.S.W. Clay-slate is occasionally met with, and near the L. del Potrero, there is white marble, rendered fissile from the presence of hornblende, mica, and asbestus; the cleavage of these rocks and their stratification, that is the alternating masses thus composed, strike N.N.E. and S.S.W. like the foliated gneisses, and have an almost vertical dip.
Northward of Las Minas, the more regular northerly ranges predominate: from this place to near Polanco, we meet with the coarse-grained mixture of quartz and feldspar, often with the imperfect hornblende, and then becoming foliated in a N. and S. line with imperfect clay-slate, including laminae of red crystallised feldspar with white or black marble, sometimes containing asbestus and crystals of gypsum with quartz-rock with syenite and lastly, with much granite.
The northern cases are numbered from 31 to 37. In the first case are varieties of felspar; in the second case are micaceous and other mineral substances; in the third case are basaltic hornblende, tremolite, &c.; in the fourth case are varieties of asbestus, which defies the action of fire; jeffersonite; jenite from the Elba, &c.; in the fifth case are various pyroxenic minerals; in the sixth case are various kinds of garnets, including the lime and chrome varieties; and in the 37th case are the silicates, including beryls, and the emerald.
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