530 J. Buskin — On Banded and Brecciated Agates. 



of the otlier, as much as any branch, of stalactitic chalcedony is of 

 the rest of the mass Nor have any of these beds ever been broken 

 at all. The whole is a tranquil determination of variously crystal- 

 lizing substances, like that of the component minerals in granite. 

 The white portions are hornstone ; the black band in each is ferru- 

 ginous, and the enclosing paste rudely crystalline quartz. 



There is, however, one grave structural difference between this 

 stone and common granite. The crystals in granite run in all 

 directions. These zones of hornstone have a more or less parallel 

 direction ; and the black band, with another narrow one succeeding 

 it, is always at the same side of them. 



I have placed the woodcut (Fig. 1) with the black beds upper- 

 most, so that the resemblance may be seen between them, and the 

 always uppermost grey beds in the highest division of Plate XV. 

 Vol. IV. But in neither case can I say that their position has been 

 influenced by gravity. For in Plate XV. it will be observed that 

 the elliptical bar of central calcite crystallizes in every direction, 

 and in this piece of hornstone, very near the portion above figured, 

 is a cavity, in which while the bands whose separation forms it, 

 retain their relation unchanged, the quartz, having now room to 

 crystallize, does so indifferently up and down, and from both sides, 

 as in Fig. 2. I do not know the position of the stone in situ. 



But though common granites show only arbitrary positions of 

 crystals, in graphic granites we have a definitely parallel arrange- 

 ment of them, somewhat resembling this of the hornstone, only 

 more regular; and in massive felspathic rock we get the same 

 deceptive resemblance of faults exquisitely defined. Fig. 3 repre- 



FiG. 3. 



Fig. 2. 



sents (of the real size : as are also Figs. 1 and 2) a portion of fels- 

 pathic rock in which two crystals of labradorite are separated by 

 apparent breccia, but really, crystalline mass, of mixed labradorite 

 and hyperstein. The oblique lines stand for this gangue (merely for 

 a symbol — there are no lines nor cleavage in the gangue itself). 

 The white spaces are pale blue labradorite, the horizontal lines 

 indicate in each crystal a sharp, exquisitely defined, zone of vivid 



