SOURCE OF ST. PETEr's RIVER. 17 



its true nature was ascertained. This marble is of the finest 

 white, with a subsaccaroidal grain, and may become of 

 great use in buildings ; it is however too fine-grained 

 for statuary purposes. An analysis of it was made with a 

 view to ascertain its purity ; it was found to consist en- 

 tirely of carbonate of lime, with little or no foreign admix- 

 ture. It certainly belongs to the primitive formation, and 

 cori'oborates the opinion we had formed at Millerstown, 

 that the primitive rocks reappear to the west of the red 

 sandstone formation ; a circumstance not stated in the geo- 

 logical observations of Mr. Maclure. It is probable, how- 

 ever, that the appearance of the primitive there is but par- 

 tial, and confined to certain localities, where it rises through 

 the incumbent strata of transition rocks. There is an exten- 

 sive cave or grotto in the blue limestone, about seven 

 miles to the east of Hagerstown, which has not yet been 

 fully explored. 



From Hagerstown to Cumberland the mountains are 

 numerous, and the works which have been executed for the 

 road have in many places laid the rock bare, so as to make 

 its structure apparent. We there see a great variety in the 

 nature of the rocks, which however are observed uniformly 

 to belong to the transition or secondary ; the former being 

 observed near to Hagerstown, and passing gradually into 

 the latter, which occur very distinctly in the vicinity of 

 Cumberland. At first, the blue limestone, with a consi- 

 derable, though varying, dip to the south-east, is seen 

 gradually passing into a slaty rock, which finally predo- 

 minates, and is a transition clay-slate, probably the Grau- 

 wacken-shiefer of German mineralogists. This however 

 is found in parallel directions, alternating, as is believed, 

 with this limestone, on a distance of several miles. After 

 which, as we approach the North mountain, a sandstone of 



Vol. I. 3* 



