12 



/. Buskin — Banded and Brecciated Concretions. 



Fig. 3. 



\J\u^\\U\\i\Uj\\um\\\ut\ur^uM.L 



by violence. But the two apparently broken portions of the band, 

 in the centre of its own loop, are simply detached crystalline forma- 

 tions of it in those places. Here, Fig. 3, is a single example of such 



an one from another 

 stone, in which the 

 enclosed banded seg- 

 ment is seen at once 

 to be concurrent at 

 its base with every 

 imdulation of the 

 surrounding belt, 

 though so trenchant- 

 ly divided from it at 

 the flanks. 



And here we have 

 to note a further sep- 

 aration of our subject 



into two branches, or, rather, into two threads of mesh (for its classi- 

 fication, like most true natural ones, is not branched, but reticulated). 

 When the bands form in several fragments in all directions, as in 

 Fig. 2, we are conducted gradually to the most fantastic structures 

 of abruptly brecciated agates. But when they are systematically 

 affected by a consistent action of crystalline power, as in Fig. 1, we 

 are conducted to the group I shall describe in the following paper 

 under the name of involute agates (I carelessly used the word 

 " conchoidal" for involute, in page 534), which seems to me, as far 

 as I have any clue to their mysterious structure, to be chiefly owing 

 to the action, in a partially fluid substance, of the great diagonal — or 

 spiral ? — force of silica. This diagonal power of, or in, quartz, is to 

 me one of the most interesting phenomena in mineral nature, both 

 in itself, and as one of a group of powers like it — wholly distinct 

 from the crystalline ones, and acting with them, or dominant over 

 them, at particular times and places, elsewhere and at other times 

 remaining entirely passive. 



Thus the growth of an ordinary quartz crystal depends on the 

 regular imposition or secretion of parallel coats, which sometimes 

 are capable afterwards of frank separation, forming "capped" 

 quartz. But the flute-beak of Dauphine is never capped. It ia 

 formed and wholly compacted under an oblique energy, which dis- 

 ciplines and guides together the hexagonal forces of the crystal. On 

 the St. Gothard the same force, instead of terminating the crystals 

 obliquely, unites them laterally, and leads them into long walls, 

 warped into 'curves, sometimes like crowns or towers. Generally, 

 when there is amianthus within crystals, the oblique force carries the 

 filaments across the crystal diagonally ; and it is very notable, as 

 regards the time of secretion of these interior deposits, that while 

 the iron oxides always arrange themselves in concurrence with the 

 coats of the crystal, amianthus and rutile never do, but shoot clear 

 through the whole body of it, if themselves long enough, and, if 

 short, root themselves on an external plane, and shoot to the inside ; 



