2 24 THOMAS L. WATSON 



III. Spherulitic rhyolite^Sam Christian gold mine, Montgomery county, North 



CaroHna. Described by J. S. Diller, American .Journal of Science, Vol. 



VII (1899, 4th ser.), p. 341. W. F. Hillebrand, analyst. Bulletin No. 168, 



U. S. Geological Survey, p. 53. 

 IV. Quartz porphyry. — Yogo Rock, sheet at head of Belt and Running Wolf 



Creeks, Little Belt Mountains, Montana. Described by Weed and Pirrson. 



Twentieth Annual Report, Part III, U. S. Geological Survey, pp. 520 £f. W. 



F. Hillebrand, analyst. Bulletin No. 168, U. S. Geological Survey, p. 125. 

 V. Quartz porphyry. — Six miles east of Ironton, Missouri. Described by E. 



Hav^^orth, Annual Report, Missouri Geological Survey, Vol. VIII, 1894, p. 



181. Melville, analyst. 



WEATHERING. 



In some exposures of the leopardite the weathered surface of the 

 rock, which is still hard and firm, presents a lusterless, dead, chalk- 

 like whiteness, the black spots of which are more or less bleached, 

 changed from black to a reddish-brown in color. This alteration 

 is brought out fairly well in Fig. 4, which is a photograph of a hand 

 specimen of the partially weathered rock, reproduced one-half natural 

 size. Bleaching of the spots is more emphasized along the top of 

 the specimen, shown in the figure (4) in the contrasted lighter color 

 of these spots to others in the same figure. When Fig. 4 is com- 

 pared with those of the fresh rock, Figs, i, 2, and 3, it is noticeable 

 that all the spots in it have undergone some leaching, as indicated 

 in their color being less intense or deep than for those in the fresh 



specimens of the rock. 



Thomas L. Watson. 



Geological Laboratory of Denison University, 

 Granville, Ohio. 



