800 



TRANSACTIONS OP THE 



altered rocks that immediately make their appearance 

 after crossing the river, and form those highlands called 

 the Blue Ridge. They extend on within 23 miles of 

 Fredericksburg. The gold belt then commences and 

 continues with but little interruption for 15 miles, when 

 we come upon the more distinctly crystallized amphibolic 

 and badly characterised granitic rocks, which extend on, 

 and are covered by the horizontal and stratified forma- 

 tions which disappear under the tide waters of the 

 river Rappahannock, as may be seen in the river be- 

 tween Falmouth and the city of Fredericksburg. 



THE BLUE LIMESTONE OF THE VALLEY OF THE SHE- 

 NANDOAH. 



This valley has been long celebrated for the fine 

 quality of the land that covers the transition beds. Its 

 surface on the whole is comparatively level ; taken sepa- 

 rately, slightly undulating. Springs abound, and the 

 water is of that variety called hard, owing to its contain- 

 ing the bicarbonate of lime in solution ; by boiling, one 

 half of the carbonic acid is driven off, which accounts for 

 the incrustations or depositions observed in those vessels 

 in which the water has been heated. The Shanendale 

 springs are situated in this valley, in Jeiferson county about 

 six miles from Charlestown. These waters have been 

 much resorted to for pleasure and health. In clearing 

 out the main spring, an abundance of fine crystals of sele- 

 nite were found a few feet below the surface of the 

 ground. These crystals may have been deposited from 

 the water, as it is known to contain this salt, with sul- 

 phate of magnesia, hydrosulphates, &c. Near Smith- 

 field^ there is a mineral water impregnated with iron, 

 which is frequently prescribed to invalids. The lime- 

 stone rock of this valley is of a variety of colours, but 

 usually blue. It is seen frequently on the surface, and 

 has a general dip to the east. The surface of this lime- 



