J^otice of the locality of Sulphate ofBarytes, ^c. 45 



speckled with minute cavities, occupied by chalcedonies, 

 agates, and quartz crystals. The valley of the brook is 

 there filled with pebbles, in which I have found blue and 

 white agates, and abundance of quartz crystals ; some near 

 ]y perfect, one an inch long, with the prism and two pyra- 

 mids, and some slightly tinged with amethyst. This valley 

 is bounded easterly by a sand-stone ridge, on the top of which 

 stands the Meeting-house; about half a mile south of the 

 M. house, in the bed of a ravine, is a bed of shale, (F) which 

 gives by friction a strong sulphureous smell. Directly east 

 of this sand-stone ridge, is a ridge of green-stone, based on 

 sand-stone; on its western face, half a mile north of the 

 road, is an interesting display of different sand-stone strata; 

 (G) the upper are not schistose, but compact and soft, mor6 

 or less tinged with purple ; the green-stone in breaking often 

 turns out nodules, which are richly irridescent on their sur- 

 face. I think them strongly impregnated with iron, and this 

 is communicated to the sand-stone or indurated clay. Be- 

 neath these strata is a stratum of free-stone, of excellent 

 quality (real sand-stone;) the rock then becomes more 

 schistose, and the lower strata are in thin layers, and very 

 brittle — breaking into minute fragments. Where the road 

 ascends the east face of this ridge, (E) the green-stone is 

 fragile, breaking into fragments of which the road is formed. 

 The fragments are porous like slag or lava ; on penetrating 

 into the rock these cavities are found occupied by zeolites, 

 or lined with minute chlorite crystals. The zeolites are of 

 two varieties; foliated fibrous and radiated; on exposure 

 to air they become opaque white, pulverulent, and are finally 

 dissipated ; leaving the rock porous. This, I presume, is 

 owing to the same decomposition which converts the coarse 

 grained granite of veins in gneiss into kaolin, of which I have 

 seen striking examples on the Schuylkill, near Philadelphia. 

 East of this latter ridge is an extensive flat of alluvial forma- 

 tion, where several streams centre from the surrounding hills 

 and mountains. Yours, &cc. 



JAMES G. PERCIVAL. 



