174 CHAP. XXIX. Quartz Rock. Reel primary Sandstone. As Quartz rock lias been either entirely overlooked or misapprehended by all systematical writers, and, until I had described it, by all observers, it is probably rare in Europe. It would be unbecoming to suppose such oversights and errors, had it occurred, as it does in our own island, in countries so often examined by geologists of reputation : though others must explain the cause of its fate here, as, in so doing, they may learn to estimate more correctly, the teachers and writers in whom they have trusted. Its history is therefore drawn solely from my own observations in Scotland; the materials having been originally pub lished in the Geological Transactions: while I may now name the few instances in which it has been no ticed elsewhere, since it thus received a leading place in the system of rocks. Von Buch describes it in Norway, and Brongniart in La Mancha ; the fictitious Ali Bey mentions it as abundant near Mecca; and it occurs near Lima and in Brazil, in tracts equalling that of Jura: though if Humboldt was unable to de termine its stratification or explain its nature, we must remember that it had not then been noticed in any geological writings. Future observers, now informed of its nature as well as its existence, will probably find this important rock much more frequent than it was suspected to be while yet undescribed. We are taught, even to see. Quartz rock, like limestone and argillaceous schist, has its counterpart in the secondary sandstones, but is not exclusively formed of the mineral whence it derives its name. The more important varieties may, how-