An. X.J Watson, Yclloiv OcJicr- Deposits of Geoi-gia. 217 



2. The contact between the ocher and the surrounding 

 quartzite is never sharp and distinct, but is marked by a gradual 

 transition from the hard quartzite to the soft ore. The transi- 

 tion-zone between the hard quartzite and the soft ocher varies 

 from a few inches to several feet in thickness between the two 

 extremes. 



3. The exceedingly irregular character of the ore-bodies 

 and their distribution in the enclosing rock furnish further evi- 

 dence. The shattered rock is cut in all directions by exceed- 

 ingly irregular branching veins of the ocher, which narrow and 

 widen, thin and thicken indiscriminately, without apparent re- 

 gard to system or uniformit}-. 



4. Microscopic study of the transition-portion of the rock 

 makes plain the relations of the ocher to the quartz-rock and 

 the mode of ore-occurrence in the rock. The iron oxide (ocher) 

 usually cuts across the quartz-grains instead of lying between 

 them. This replacement process is never complete, but all the 

 ocher contains more or less free quartz-grains distributed through 

 it. The grains are very irregular in outline, which distinguishes 

 them from ordinary quartz- or sand-grains, and they were evi- 

 dently formed from solution. 



5. Finally, the replacement-hypothesis is strengthened by 

 the general appearance of the rock which affords in places evi- 

 dence of solution and redeposition of the silica. Small cavities 

 are frequently observed penetrating the quartzite, and lined with 

 very small crystals of quartz deposited from solution. Also, 

 the skeleton of silica holding the ocher together and the sand- 

 grains disseminated through the purer beds of soft ocher appear 

 to have been derived by deposition from solution, rather than 

 to be composed of grains of the original rock. 



The source of the iron oxide, and the solution of the quartz 

 of the rock and its replacement by the iron oxide (ocher) have 

 been previously discussed in some detail by Hayes, ' and need 

 not be repeated here. After a microscopic study of a large 

 number of thin sections of the ocher-charged and the ocher- 



^ Trans. ^ xxx,, 403. 



