Annual report . olved away. The rock has a high specificgravity and in almost all cases is rusty in color. The thin sectionshows large, irregular pleochroic brown and green hornblendes, withsome pyroxene. Magnetite inclusions are numerous and this min-eral also occurs abundantly along numerous cracks, sometimes inassociation with serpentine borders or fillings. The ledges of the quartzite are more numerous and more ex-tensive than those of either of the other rocks. Its apparent widthis about 75 or 100 feet. It is thin-bedded and steeply inclined. Itis very similar to the basal quartzite as se
Annual report . olved away. The rock has a high specificgravity and in almost all cases is rusty in color. The thin sectionshows large, irregular pleochroic brown and green hornblendes, withsome pyroxene. Magnetite inclusions are numerous and this min-eral also occurs abundantly along numerous cracks, sometimes inassociation with serpentine borders or fillings. The ledges of the quartzite are more numerous and more ex-tensive than those of either of the other rocks. Its apparent widthis about 75 or 100 feet. It is thin-bedded and steeply inclined. Itis very similar to the basal quartzite as seen at certain places andappears to belong to that formation. It may be followed distinctlyfor several hundred feet. At the north and south these types give way to the characteristicgneisses of the mountains. The exact field relations of these rocks are very obscure. Nocontacts could be found. Seemingly the only clue to their age andrelationships is to be obtained from the structural features and BA-STITE. QUARTI ROCK TE- BASIC GNEISS E- F?U PT»VE- Fig. ii Sketch map to show the general relationships at Hortontown. Scaleapproximately 200 feet to the inch. GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 39 Interpretation. The possibility suggested itself that some ofthese rocks might be members of the basal gneiss series. Thequartzite, however, is almost certainly Paleozoic in age. The blackhornblende rock has the characters of a basic eruptive. The greenserpentine variety gives little idea of its original character, but it isapparently not an altered pyroxenic rock. The southwestward continuation of the reversed fault along thenorthwestern slope of the eastern gneiss mass would apparentlyintersect the fault on the east of Shenandoah mountain in thisneighborhood. The latter scarp is only a short distance west of thequartzite. This intersection would have been a most favorable pointfor an igneous intrusion. Some of the basal Paleozoics were evi-dently caught at this inte
Size: 1541px × 1621px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectscience, bookyear1902
