JULIEN, GENESIS OF ANTIOORITE AND TALC ' 37 



silicate; and then the main solution, or mixture of the two components. 

 During consolidation and contraction of the last deposit, disassociation 

 of the hydrate took place by diffusion into the shrinkage crevices near the 

 middle of the vein. In fact, however, the separated deposits here found 

 •on the walls are probably, like those next to be described, derivatives from 

 mixed solutions, by disassociation higher up the vein. 



The most complex variety of composite veins is that represented in the 

 illustration (Plate VI) and ordinarily found in proximity to laterite 

 rich in magnesian silicates. It consists of a lamellation, in abundant 

 repetition, of thin alternating sheets of chrysotile and retinalite, the 

 "thickest near the vein-wall and thinning outwardly ; the first very thick 

 layer of retinalite on the vein-wall is absent, having been broken from 

 "the specimen. In structure and development the variety is essentially 

 identical with the lamellation of antigorite ("eozoon") in dolomitic lime- 

 stone at Grenville, Canada, and other localities, although there the ma- 

 terial of alternation with retinalite is calcite in place of chrysotile. In 

 •each case, I have concluded, a rhythmical process of unilateral vein depo- 

 sition from laterite solutions has originally taken place — every pair of 

 lamellae comprising a film of colloid, magnesium hydrosilicate, with one 

 'of crystalloid, magnesium hydrate here and calcite in the Canadian oc- 

 currence, separated from the colloid by dialysis. 



The rhythm of deposition has apparently been due to limitation of the 

 flow into the vein fissure of the mixed solution of the two magnesian salts 

 in meteoric waters to a certain period of accumulation, perhaps the rainy 

 reason of the year. After spreading upon the surface of the wall, dis- 

 association began, the colloid being left clinging as a new coat upon the 

 wall, while from its outer boundary — perhaps through a dried film serv- 

 ing as a septum — the ciystalloid magnesium hydrate became diffused 

 more or less completely by dialysis and so formed the companion coat of 

 each pair of alternations. The amo-rphous magnesium hydrate readily 

 •crystallized into brucite, and this, by subsequent pressure — perhaps by 

 rock strains, through expansion in neighboring portions of the mass — 

 was converted into its fibrous variety, nemalite. Other fissures have been 

 opened by contraction of the rock more or less transversely to this lamella- 

 tion, but these have been generally filled with magnesium hydrate, amor- 

 phous and crystalline, as simple veins, changed in turn into nemalite by 

 rock strains. 



By later silicification or alteration under thermal conditions, all these 

 lamellae and transverse veins have become altered — nemalite into chryso- 

 tile-asbestos and deweylite into massive antigorite, in part retinalite. 



