. Scientific survey of Porto Rico and the Virgin Islands. Scientific expeditions. 136 SCJESTIFW SURVEY OP PORTO RICO agirloiin;rates. The color ^ black, dark gray or olive green; where ihu grained, and, as the te^xture becomes coarser, tJie (H)b>r becomes mottle! hecauKi' of the fragiiients, wliieh may be black, gray, green, dark piirpU' •:?.!? dull red. .Many of the lava flows contain tulTaecous nu-itcrial which iiiii\ to as much as dO per cent, laidcr tht* niicrostiopc thx' tuffs to-be divisible into two classes, eryslal tuffs ajid lithic tuffs. The crysini tulTs (Fi
. Scientific survey of Porto Rico and the Virgin Islands. Scientific expeditions. 136 SCJESTIFW SURVEY OP PORTO RICO agirloiin;rates. The color ^ black, dark gray or olive green; where ihu grained, and, as the te^xture becomes coarser, tJie (H)b>r becomes mottle! hecauKi' of the fragiiients, wliieh may be black, gray, green, dark piirpU' •:?.!? dull red. .Many of the lava flows contain tulTaecous nu-itcrial which iiiii\ to as much as dO per cent, laidcr tht* niicrostiopc thx' tuffs to-be divisible into two classes, eryslal tuffs ajid lithic tuffs. The crysini tulTs (Fig. 12) have the. composition of an augitc andesite j)orpliyry suiil eontain, taking tlic average, about 20 per cent augiie, 4t) per cent andcsin. ftddspar, 20 per c;eni magn,etite and 20 per cent of secondary prodiieis,. Homctijnes tiiey show a faintly streaked, diaraerer, as it they wi-re y tlieir dr\elopmeiit, created the binding ni: lerial of the roek. At times there arc small |)Hen(h)vesieular spaces lid' with zeolites, natrulite. Tfiese spa<'cs arc about 1 mm. in s^ and are pruhablv produced by inhltration ami metasomatie rcplac(;jni-' by zeolites. In eomposiiion, the litlde tulfs (Fig. Kt) arc rather siujplc. They n osiwlly conrpo-ed of rehlspathic andesitcs or augite an.(lesiles. The 1-. tnral tvpes. however, are numerous and as many as fiftet^n may l)0 jnv-'. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original New York Academy of Sciences. New York, : The Academy
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectscienti, bookyear1919
