GEOLOGICAL SOCIETY OF PENNSYLVANIA. 



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violet, the amygdals containing green crystals and some- 

 times white, and though not as prevalent as in those 

 rocks described as argillo-porphyries, bear so great a re- 

 semblance that we cannot avoid believing them to be of 

 similar origin. 



In a greenish blue, slaty, altered rock at about fifteen 

 miles from Warrenton, a trap dyke or vein juts up and 

 limits distinctly the talcose slates of the gold region. A 

 portion of this trap dyke is a heterogeneous mixture of 

 specular oxide of iron, silicious grit and a petro-silicious 

 substance of a green colour, passing imperceptibly into 

 the homogeneous traps that bound it on either side. The 

 talcose shales, as they approach these traps, are modified ; 

 and there being no distinct line of demarcation between 

 the shales and the traps, we might compare this alteration 

 to that of a stick of wood, one end of vv^hich was thrust 

 into a fire and charred. The gradation from wood to 

 charcoal is evident, though not sudden. 



A copper mine was formerly worked not far from this 

 spot, but to what extent we are not able to say. 



In proceeding on over the talcose slates, &c. of the 

 Gold Belt, numerous quartz veins have been observed to 

 contain gold, when you come upon steaschiste with ami- 

 anthus passing into jade. One section, then, traverses 

 the Union Gold mining property, the minute details of 

 the stratification of which we present in a separate and 

 enlarged section. 



From the Union mines, proceeding with our section 

 eastward, talcose and chlorite slates, accompanied by 

 protogine and various modifications of rocks of this cha- 

 racter, occupy a breadth of eight miles from the Union 

 mines. On the Rappahannock the protogine rocks occu- 

 py a breadth of nearly a mile, succeeded by a belt of this 

 same rock passing into a sienitic granite, having quartz 

 veins intersecting the mass. 



Garnet schists, talcose schists, and the auriferous 



