ART. 2. PETROLOGY AT GOOSE CKEEK SHANNON. 57 



On the same specimens there are also silky tufts of white fibers of 

 the same mineral which were better suited for a determination of 

 the optical properties. These are associated with calcite, laumontite 

 and albite crystals. They are definitely inclosed in calcite crystals 

 and are clearly older than the laumontite but seem later than the 

 water-clear prismatic albite crystals. One sheet of the papery variety 

 was seen to overlie a layer of the chlorite last described and to 

 underlie stilbite. This sheet of hornblende contained entangled 

 epidote crystals. 



The thicker fibers from these tufts show a suggestion of very pale 

 blue green color under the microscope with pleochroism. They are 

 biaxial negative with 2V large, dispersion r < v weak. The extinction 

 Zac is inclined 15° maximum, the mean of many measurements. 

 The refractive indices are a= 1.648, 0= 1.668, 7= 1.676, all variable 

 .005. Birefringence 7 — a =.028. 



The mineral fuses in very thin splinters in the blowpipe flame to a 

 black glassy bead which is strongly magnetic. 



This fine fibrous hornblende is widely distributed and has been 

 mentioned as being noted in thin sections. A specimen of hydro- 

 thermally altered aplite shows a later seam of diopside, along which 

 are small open spaces containing this white hornblende in fine silky 

 fibers on which are impaled crystals of epidote and axinite. 



Although such asbestiform amphibole has not been frequently 

 noticed in association with the zeolites of traps, Col. W. A. Roebling 

 loaned the writer a specimen labeled paligorskite, regarding which 

 he writes the following note: "This paligorskite came from the old 

 Bergen Hill R. R. tunnel many years ago. I have forgotten who sent 

 it to me — probably Rev. Dr. Spencer of Tarrytown." 



This specimen contains small tufts of snowy fibers exactly like 

 those of the Goose Creek specimens. These are interspersed with 

 perfect stilbite crystals and larger calcites on a layer of drusy quartz. 

 The base of the specimen is coarse slickensided diabase, the augite 

 of which is chloritized. The slickensides are coated with diabantite 

 varnish. 



Under the microscope these fibers show a birefringence which 

 reaches a maximum in first order yellow. They are biaxial negative 

 with 2V large, axial plane parallel with the length. The extinction 

 is inclined, Zac about 16° average. The indices of refraction are 

 a= 1.652, |8= 1.672, 7=1-675, 7-a=.023. 



The New Jersey amphibole is, therefore, almost identical in every 

 detail of property and occurrence with the Goose Creek mineral. 



Scattered through the scaly chlorite, which forms the first coating 

 on the altered rock of an east-west shear zone, as described above,. 



