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It lies, near Malpaso, on green slates, steatitic, mingled with hornblende, destitute of mica and grains of quartz, dipping, like the grunsteins, 45 degrees toward the north, and directed, like them, 75 degrees north-west. At Piedras Azules these slates, mingled with hornblende, cover in concordant stratification a blackish-blue slate, very fissile, and traversed by small veins of quartz.
We proceeded down hill during six or seven hours; and we skirted the Cerro de Flores, near which the road turns off, leading to the great village of San Jose de Tisnao. We passed the farms of Luque and Juncalito, to enter the valleys which, on account of the bad road, and the blue colour of the slates, bear the names of Malpaso and Piedras Azules.
Sometimes we seem to see serpentine, sometimes grunstein, and sometimes dolerite and basalt. The arrangement of these problematical masses is not less extraordinary. Between San Juan, Malpaso, and Piedras Azules, they form strata parallel to each other; and dipping regularly northward at an angle of 40 or 50 degrees, they cover even the green slates in concordant stratification.
With respect to the green slates of Malpaso, which have all the characters of transition-slates, they are identical with those which M. von Buch has so well described, near Schonau, in Silesia. It forms perhaps a subordinate stratum in the slates of Malpaso. On some points we think we observe one passing into the other.
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