128 
ANNALS NEW YORK ACADEMY OF SCIENCES 
with a thin dark colored film and show that the split followed a seam which 
was almost imperceptible before it was thus disclosed. 1 
To study the conditions existing in a crevice or cavity containing minerals 
previously undisturbed, it is necessary for the investigator to be present 
when it is first exposed directly after a blast. Although I have spent many 
days in quarries, I have been favored with few such opportunities, perhaps 
a dozen in all, and have invariably found the contents of the cavity saturated 
with moisture. In some cases the crevice or cavity ivas filled with a viscid 
material resembling paste in appearance and covering clusters of superior 
crystals. 2 I have seen cavities of various sizes, partly or entirely filled with 
water and often containing no mineral deposit whatever, exposed by the 
sledge hammer in apparently solid trap. 
Probably the water reaches such cavities through microscopic crevices 
although Bischoff 3 credits it with penetrating through the pores of the rock. 
Occasionally a cavity is filled with material resembling wet snow, covering 
groups of crystals, sometimes on a lining of pectolite. This material is 
sometimes thaumasite penetrated by concretions and needles of pectolite, 
sometimes apparently laumontite, in microscopic crystals. In some cases 
a narrow cre\ r ice will be lined on opposite sides with two different minerals 
as heulandite and ealeite, almost in contact, but each free from the other. 
In other cases the crevice will be filled solid, A\ T here it is narrow, with a single 
mineral, and where it is wider this divides into linings with finely crystallized 
faces. 
The deposition of two or three of the trap minerals synchronously or in 
close alternation produces occasional cryptocrystalline masses attractive in 
appearance, but having the composition and structure of a rock rather than 
a mineral. Such would be a solid mass composed of needles of pectolite 
or natrolite carrying parasitic crystals of apophyllite, gmelinite or calcite as 
illustrated in Plate XI, Figs. 3 and 4, and Plate XII, Figs. 1 and 2. Some¬ 
times, as in Plate XI, Fig. 3, the parasitic mineral is distinguishable through¬ 
out the resulting solid, but usually the mass appears, deceptively, to consist 
only of the predominant mineral, while it approximates a solid solution in 
character, as is the case with much of the pectolite from Woodcliff, N. J. 
(Plate XIII, Fig. 3) in which many of the needles are invested with micro¬ 
scopic crystals of calcite. To this may perhaps be attributed the excep¬ 
tionally strong yelloAv fluorescence and tribophosphorescence of the 
Woodcliff and some other pectclites, as the thermo- and tribophosphor- 
1 See G. Bischoff, op. cit., Vol. 1, p. 10. 
2 A gelatinous substance having the composition of chabazite has been noted between cal¬ 
cite crystals by Renevier. E. S. Dana, Syst. Min., p. 590. N. Y., 1S92. 
3 Op. cit. Vol. 1, p. 54. 
