JULIEX, GENESIS OF ANTIGORITE AND TALC 33 



AUeration, to express the interchanges and consequent new formations, 

 with great loss of water, which take their birtli in a more deeply seated 

 region. The common products are the mag-nesium hydrosilicates of the 

 second type (talc, antigorite), hardened deweylite, forms of limonite, 

 gothite, turgite, hematite, etc. 



Decomposition (Zersetziing of Eoth), to express the molecular disso- 

 ciation, still more complex interchanges, and still greater to complete 

 dehydration, which have ensued within the zone of anamorphism. Ex- 

 amples of these products are periclase, spathic magnesite, dolomite, 

 siderite, breunerite, regenerated olivine (boltonite, forsterite), specular 

 iron, magnetite, etc. 



In regard to the term "hydrometamorphism," whether in the sense of 

 Lindgren, referring to the action of meteoric or vadose waters, or in that 

 of G. P. Merrill, referring to the action of waters from deep-seated 

 sources or from magmas, I find no application for it below the belt of 

 weathering. There only has originated the highest hydration; below it, 

 every change has been attended by progressive loss of water. 



Genesis of Chkysotile and Eetinalite 



In Plate VI, a well-known laminated variety of asbestos-rock from 

 Thetford, Canada, is presented. Here lie the leaves, silver and green, in 

 long succession, of the book of the history of asbestos, waiting for inter- 

 pretation of the mystery of its origin. 



If "serpentine," as long believed, is a colloid, incapable of crystalliza- 

 tion, is this fibrous chrysotile but an alteration product from asbestiform 

 amphibole or bronzite ? Or are these fibers only "serpentine" wires, pro- 

 truded through pores in the vein walls, like those of metal in the arts? 

 Or, along fault planes, has the serpentine been rolled out and sheared 

 into these silky threads? Or, if there be a cn-stalline paramorph of 

 amorphous "serpentine," is this its fibrous deposit from lateral infiltra- 

 tions into rock fissures? Is it possible that these have been generated 

 by diamagnetic secretion along the vein walls, expelling into the median 

 fissure of the vein the feebly magnetic brucite, poor in iron, and the 

 diamagnetic calcite? Or are the fibers in fact capillary or acicular crys- 

 tals either of "serpentine" itself or of its paramorph, thrust from one 

 wall to the other, or grown simultaneously inward from each wall ? 



It is doubtful whether any one of these conjectures has proved satis- 

 factorv even to its author. 



Toward solution of this part of Delesse's enigma, in my turn, it re- 

 mains to sketch some of the migrations and transformations of the 

 magnesian derivatives from rock decay, as they oozed downward from 



