36 ANNALS NEW YORK ACADEMY OF SCIENCES 



Composite Veins 



While the separate deposition of both niMgin'siuiii hydrate and coUoid 

 deweylite has frequently taken place, as described, in siin))Ie veins of each 

 7nineral, nevertheless their normal niid |)rol)at)]y nion' coininon ino<le of 

 conveyance from hitcritc downward has Jjccn in intiMinixture. Com- 

 posite veins have resulted by separation of 'successive deposits of each 

 from this mixture, niul not, :is mi_t,dit first he judged, by a series of de- 

 posits upon each wall, now of one mineral, now of the other, in alternation. 



A simple form lias consisted of a vein with wall coatings of brucite 

 or nomalite, with a middle sheet of deweylite. \\\ silicitlcation, the wall 

 coatings have passed into iihroiis deweylite, and this, by later alteration, 

 into chrysotile-asbestos, with a sheet of massive antigorite or retinalite 

 intervening, as at Portchester, New York, etc. 



The reverse order of arrangement has been also observed, with sheets 

 of massive antigorite or retinalite (i. e., originally deweylite) coating the 

 walls, and a central sheet of brucite, nemalite and sometimes calcite, as 

 in the Vosges ; or with a central sheet of nemalite, in part chrysotile, as 

 at Hoboken. 



A proof of the above suggested intennixture of the two magnesian 

 components is yielded from study of analyses of retinalite. A specimen 

 "associated with eozoon" at Calumet, Quebec, gave T. S. Hunt the follow- 

 ing results: silica, 41.20; magnesia, 43.52; ferrous oxide, 0.80; water, 

 15.40; 100.93. My recasting of this reveals the following constitution: 

 antigorite, 83.90; deweylite, 11.76; brucite, 5.24. That is to say, a nota- 

 ble portion of each of the original magnesian components has escaped 

 alteration and remains intermixed with the antigorite. 



An interesting example of such intermixture has been observed in a 

 symmetrical asbestos vein, two inches in width, in dark green serpentine 

 containing particles of chromite, on lot 13, Eange V, Thetford, near Rob- 

 ertson station, Canada. ^^ The first deposit on each wall has been a thin 

 layer of dark blue antigorite (originally deweylite) "with grains of 

 chromic iron"; then a layer of chrysotile (originally brucite), with fibra- 

 tion normal to the wall ; then a thin layer of pale-green retinalite (orig- 

 inally deweylite) ; and a central sheet, about \l inch thick, of dark blue 

 antigorite (originally deweylite mixed with magnesium hydrate), along 

 the middle of which run minute seamy partings of chrj'^sotile (originally 

 brucite) parallel to the plane of the vein. 



A succession of four passage solutions of magnesia is here indicated: 

 first, the colloid hydrosilicate ; then the hydrate; then a.gain the hydro- 



'» p. CfRKEL: Asbestos, p. 28, Fig. 0. Ottawa. 1S05. 



