. Bulletin of the Department of Geology. Geology. 284 University of California Publications in Geology [ present, and the amount of iron oxide which they contain. In texture they range from loose porous varieties which will adhere to the tong'ue, up to dense compact varieties which look like wood opal. The bedded cherts of the Monterey group break with rather jagged sur- faces. They seldom show the smooth conchoidal fracture of the Franciscan cherts, probably due to some difference in the condition of the silica which composes them. They show a dull earthy luster and not the waxy luster
. Bulletin of the Department of Geology. Geology. 284 University of California Publications in Geology [ present, and the amount of iron oxide which they contain. In texture they range from loose porous varieties which will adhere to the tong'ue, up to dense compact varieties which look like wood opal. The bedded cherts of the Monterey group break with rather jagged sur- faces. They seldom show the smooth conchoidal fracture of the Franciscan cherts, probably due to some difference in the condition of the silica which composes them. They show a dull earthy luster and not the waxy luster characteristic of the Franciscan cherts, and of the flinty cherts of the Monterey. One very characteristic feature of the bedded cherts of the Mon- terey is the minute lamination. Each bed of chert shows a great number of fine bands of different color, or different shades of the same color, parallel to the bedding of the chert. These bands are so thin that there may be twenty or thirty of them in a layer of chert an inch Fig. 11. Discordance of lamination within a single bed of chert. in thickness. This lamination of the chert beds is almost universal, but some bedded white cherts fail to show it and occasionally a black bedded chert is not laminated. In spite of the fact that this lamination is so well developed and is nearly parallel to the bedding, the cherts show very little tendency to cleave along the laminae. Occasionally there may be a slight tendency in this direction, but it is very exceptional, and as a general rule, the chert beds break up into fragments of irregular form along cracks which run transversely to the bedding planes. As revealed in cross sections of the chert bed, the laminae are indi- cated by bands of different color. These often run nearly parallel with the bedding of the chert and are remarkably regular, though there are numerous exceptions to this statement, some of which are rather peculiar. In certain specimens a sort of false bedding is shown by
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