l886.] NEW-YORK MICROSCOPICAL SOCIETY. 91 



variegated by delicate whitish efflorescence within the inter- 

 stices. This efflorescence was found to penetrate to a depth of 

 about I to 2 centimetres below the surface along the fibres, 

 and even to the very centre of the nodule, at a depth of 8 centi- 

 metres along certain widened fissures among the fibres. The 

 material differed little from that of similar fibrous nodules from 

 Galena, Illinois ; Linden, Wisconsin, and other localities. Va- 

 rious fragments of this material were mounted for examination 

 by reflected light, and for this purpose, low magnifying powers, 

 up to 200 diameters, were found sufficient, with the help of the 

 plane mirror of a Sorby reflector. 



The following materials were thus examined : — 



A. A fibrous plate of the fresh and brilliant material from the 

 interior. The surface of this natural fragment was divided up, 

 through the fibration, by strongly marked lines, sometimes per- 

 haps indicating open fissures, 0.033 to 0.134 mm. apart. Within 

 these, in many places, a still finer lining occurred, the lines be- 

 ing sometimes only 0.014 mm. apart. These finer lines, coincid- 

 ing with the cubic cleavage, were sometimes parallel to the main 

 fibration, sometimes perpendicular to it. Elsewhere, they were 

 commonly arranged obliquely, at an angle of 45° to 53° from the 

 general direction, sometimes even in two sets, passing obliquely 

 off in opposite directions from a median line ; these latter 

 oblique lines doubtless mark the octahedral cleavage of pyrite, 

 often greatly distorted by pressure, and even, thereby, rendered 

 curvilinear. A want of homogeneity was suggested by a num- 

 ber of bright, angular, yellow particles and grains scattered over 

 the white and duller surface ; their size usually varied from 

 0.013 to 0.084 iTim. 



B. A fragment from a plane at right angles to that of A, pre- 

 senting the polished mammillary, and curved surface from the 

 cross-fracture. The entire surface was found to be not uniform 

 as it appeared to the eye, but seamed and slightly roughened by 

 short fissures, marking the cubic cleavage, running at right 

 angles to each other, but rarely intersecting, dividing up the 

 surface into square spaces about o.oi to 0.015 ^'"^' o^ ^ side. 



The same bright-yellow grains appeared here and there, as in 

 A, but mostly as lines or thin branching veins, apparently the 

 edges of films of yellow material, enclosed in the paler-colored 

 pyrite. 



