30 ANNALS NEW YORK ACADEMY OF SCIENCES 



Here, as in most equations Vhich have been suggested in discussions 

 of mineral genesis, the initial colloid condition of most products of min- 

 eral decay has been disregarded. Besides this, the minerals assumed ap- 

 parently as derivative within the belt of weathering — antigoritc, magnet- 

 ite, hematite — are those which have surely taken their birth or acquired 

 crystalline form in a lower and thermal belt'ot alteration. The difference 

 of view on the common products of olivine decay (omitting double salts) 

 within the belt of weathering may be contrasted as below : 



By common hypofhem. By observation. 



Quart., hyalite, opal \ ^''^'^ '1"'"''' '»y<l'-'>t««; an.orphous hyalite, 



'^ ' -^ ' ' I. chalcedony ; quartz. 



r Colloid or aiiiorf)hous inan<j;anese hydrate, 



Pyrolusite -| hydrocarbonates, carbonate and hydrt-. 



I silicates; j)yrolasite. 



.^ .... ■ •. j Colloid or amorphous nickel hvdrates, hvdro- 



"Uentnite, gamiente ^ carbonates and hydrosilicat"es (conna'rite). 



C Colloid ferric or ferroso-ferric hydrates, hy- 



-Siderite, magnetite, hematite \ drocarbonate, carbonate, hydrosilicate, in 



I part amorphous; siderite. 



! Colloid or amor[)hous calcium carbonate, 

 hydrocarbonates and hydrosilicates; cal- 

 cite, dolomite. 



i Amorphous magnesia; amorphous mayrne- 

 sium hydrate, hydrocarbonates, carbon- 

 ates; brucite, hyclromagnesite, magnesite. 



. ^. ., . , , ,.. . ,•, (Colloid magnesium hydrosilicates (dewey- 



Antigorite,talc,deweyl.te,sepiolite. [ y^^^^ sepiolite). in part amorphous. 



In the equations above given to illustrate the supposed direct conver- 

 sion of olivine into antigorite, the calculated volume changes varied from 

 -|- 12 to -j- 37 per cent. To this expansion and subsequent shrinkage, the 

 phenomena of fracture, gliding, slickensiding, etc., observed in many 

 bodies of serpentine, have been attributed by G. P. Merrill and others. 



Dual Processes in Genesis of Talc and Antigorith 



The object of the present paper is to distinguish and deline my con- 

 clusions (without the evidences) concerning the dual processes as well as 

 dual regions of alteration — first, the belt of weathering, ami hil<M- the 

 lower region, connected with development of both tale ami antigorite 

 from olivine. 



Three other minerals, hitherto treated merely as interesting accessories 

 during development of talc and "serpentine" — viz., brucite, sepiolite and 

 deweylite — now offer their claim as es.sential elements, in amorphous or 

 colloid form, to the genesis of the two minerals in question. The key to 



