The most striking peculiarity is the great prevalence of vesicular trap and amygdaloid with nodules of zeolite or agate covered with green earth. Beds of volcanic ash are also very common, differing little from the basaltic lavas with which they are interstratified, but their brecciated structure can always be readily detected. Occasionally pumice is found in ash beds, but with interstices filled up as in amygdaloid. Here and there, throughout the trap, beds of red bole occur, generally a foot or two thick, sometimes containing scorix, in which case they cover the upper portion of a basaltic flow, into which they appear to pass. Cracks and hollows are frequent, and the finest crystals are sometimes found in them. The principal minerals found in crevices and cavities, and forming the nodules of amygdaloid, are rock crystal, seldom amethystine, with the other varieties of quartz, such as agates, jasper, heliotrope, and chalcedony. Among the anhydrous carbonates, calcite (Iceland spar) is very abundant. Of the zeolitic hydrous silicates, thomsonite, natrolite, galactite, and stilbite are common; and among the other hydrous silicates laumonite, prehnite, and apophyllite; while the green mineral glauconite is very prevalent in the vesicular and amygdaloidal traps.
