16 EXPEDITION TO THE 



formation which was received, it would appear probable, 

 that the ore has been worked, in one place at least, on a 

 vein running nearly east and west. The rock, as has been 

 observed, is a talcose slate, which in some places appears to 

 be penetrated with copper pyrites. These mines all lay in 

 a hill known by the name of Jack's mountain ; upon the 

 top of which a porphyritic rock occurs. The crystals are 

 of feldspar ; the cement is of a red colour, and appears to 

 be compact feldspar, ( pett^osilex palaiopetre of de Saus- 

 sure ;) besides the crystals of feldspar, there are some of 

 quartz and probably of mica. This porphyry appears 

 principally upon the east side of the mountain towards the 

 top — no indications of stratification were observable. The 

 porphyry constitutes probably a subordinate formation in 

 the talcose slate which reappears on the crest of the hill, 

 and is there very abundantly studded with small crystals, 

 which are presumed to be epidote. In descending on the 

 west side of Jack's mountain, the blue limestone reappears 

 very distinctly stratified, the strata running north-east and 

 south-west, it dips in most places about 80° to the south- 

 east. The dip varies however, being only in some places 

 about 30°, as may be very distinctly observed in the exca- 

 vations made for cellars, &c. at Hagerstown. 



This town is pleasantly situated in Washington county, 

 Maryland, on the great turnpike road which leads from 

 Baltimore to Cumberland. We saw here specimens of the 

 white marble which occurs at Boonsborough, about ten 

 miles south-east of Hagerstown. It is said to exist there in 

 considerable quantities on the west side of the South moun- 

 tain not far from its foot. It was at first mistaken for gyp- 

 sum by the people in the neighbourhood, and very abun- 

 dantly applied to manure their lands, and it was only after 

 its inefficacy had been demonstrated by experience, that 



