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escence of certain tremolites have been attributed to a somewhat similar 
inclusion of dolomite. 1 
In several localities a mineral occurs in flexible filaments sometimes as 
fine as hair. 2 One or more of these, perhaps two centimeters in length, 
may project from a face of a crystal of datolite or calcite, or they may be 
attached in clusters directly to the trap or to a film of diabantite upon the 
trap as in the example from Snake Hill illustrated in Plate XII, Fig. 3. 
Often they cross a cavity between adjacent groups of datolite crystals inter¬ 
secting in all directions. Each filament frequently supports a series of 
crystals of calcite, datolite, apophyllite or other minerals like beads upon a 
thread or dew drops on a spider’s web, ranging in size from microscopic to 
macroscopic and with all faces complete. 
A large quantity of such a filamentary mineral was recently found by 
Mr. James G. Manchester, of New York, thus associated with datolite in a 
nearly vertical crevice in the Erie Railroad cut through Bergen Hill. In 
part it was massed together resembling asbestos, in part disposed as above 
described (Plate XII, Fig. 4). Throughout it was invested with crystals of 
various sizes and kinds, a large quantity of which, chiefly datolite, fell from 
the cavity like sand when it was disturbed. Many of these were euhedral 
and probably had been supported on the filaments. 3 The matted filaments, 
when mounted in balsam, were found to entangle a multitude of microscopic 
crystals of several minerals easily distinguishable from each other in polar¬ 
ized light. At Great Notch a similar filamentary mineral has been noted 
(but rarely) forming fringes on microscopic plates of a black mineral. 
Commonly all these minerals are separated from the trap by a thin film 
of a material varying from gray to greenish black in color and often having 
the feel of talc (Plate XII, Figs. 2 and 3). Apparently similar material of a 
greenish black color occasionally fills small crevices in the trap and in many 
cases occurs in large quantity, as at Woodeliff (Guttenberg) where, together 
with prehnite invested with beautiful microscopic crystals of other trap 
minerals and numerous large crystals of such minerals, it occupies the 
interstices between fragments and sheets of partly decomposed trap that 
fill a nearly vertical fault or shear zone about a meter wide in the Palisade 
1 Bournon, quoted by Parker Cleveland: Elem. Treatise on Mineralogy and Geology, 
p. 323. Boston, 1816. 
2 This is probably a fibrous natrolite which according to Mr. F. A. Canfield was called 
fibrolated-natrolite by Dr. A. E. Foote. This name is however not mentioned in Dana, Syst. 
Min., New York, 1S92. Fine specimens from Bergen Tunnel No. 2 are in the collection of Mr. 
Canfield at Dover, N. J. 
3 Since this paper was presented, these datolite crystals have been described by W. E. 
Ford and J. L. Pogue, Am. Jour. Sci., IV, xxviii, p. 187, Aug., 1909. 
