In pressure-modified gneisses and schists certain minerals are often distinctly secondary in formation; actinolitic hornblende replaces ordinary hornblende in a gneiss, as on the southern side of the St. Gotthard Pass (31), or in a dark mica-schist, as in the Binnenthal (32), or a tremolite appears in marble near the Campolungo Pass (33). A mixture of crushed hornblende and felspar gives rise to a biotite, small flakes of which may be built, like bricks, into a newly-formed large crystal of hornblende, especially towards its exterior (34). Glaucophane in hornblendic rocks, such as diorites and eclogites, is often a secondary mineral (35), some constituents derived from a crushed soda-felspar having combined with those of the original hornblende. Rather large biotites have formed in a dark mica-schist in the Binnenthal, and here also some of them have been developed at right angles to the main pressure, but others in the direction of it (36). Scales of chloritoid, sometimes a third of an inch in diameter, are secondary formations in some gneisses and chloritic schists, and kyanites in some micaceous schists suggest a possible reconstruction of an original mineral. Chlorite itself is a mineral of secondary origin, and such rocks as smaragdite-euphotide (37), saussuritic gabbro, and possibly even ordinary gabbro are all more or less altered from their original condition, and in some at least of these cases pressure may have been a factor in the change.