58 Pratt — Origin of the Corundum associated with 



f. Green chlorite. As far as observed, always present, and 



varying from 1 to 12 inches in width. 



g. Enstatite; in places hard and compact, several feet wide; in 



other places only a few inches wide, usually merging into/i. 

 h. Talcose rock, usually fibrous, varying from a few inches to 



several feet in thickness. 

 L Dunite, more or less altered, friable and stained with ferric 



oxide. 

 j. Dunite, apparently unaltered, quite extensive. 



Between h and i a seam of yellowish clay is sometimes 

 observed which often contains a narrow seam or fragments of 

 chalcedony. 



From what could be learned from actual observations and 

 inquiry among the miners, c and d are sometimes absent, and 

 when this is the case, e, a mixture of chlorite, vermiculite 

 and corundum, is seemingly in direct contact with b. The 

 chlorite, however, on the dunite side of the section is constant. 

 The thickness of the several zones (a, &, <?, etc.) in such sections 

 varies greatly at different places ; and the distance across such 

 sections may be said to vary at different points, even in the 

 same region, from a few feet to 30 or 40 feet. The accom- 

 panying diagram (fig. 5) represents the cross section of a con- 

 tact vein observed at Corundum Hill. 





dc b 



n'l 



i 





"i 



1 I 



ililiilili 



a 



In the diagram, fig. 5, a represents gneiss, apparently fresh 

 and unaltered, passing into b, which has somewhat the appear- 

 ance of the unaltered gneiss, but is so decayed that the parti- 

 cles readily separate from each other ; c, narrow zone of 

 vermiculites that sometimes is entirely lacking; d, green 

 chlorite, clinochlore, partially decomposed and forming the 

 vermiculites of c ; e, the corundum-bearing zone, a mass of the 

 green chlorite with crystals and fragments of corundum dis- 



