SOURCE OF ST. PETER S RIVER. 13 



purchased horses in exchange. This part of the journey was 

 performed in eleven days. The usual route through Lan- 

 caster, Columbia, York, and Gettysburg, was travelled. 

 Here they left the Pittsburg turnpike road and reached 

 Hagerstown in Maryland by a cross road ; from Hagers- 

 town they continued along the Maryland turnpike road to 

 Cumberland, where it unites with the national road, upon 

 which they travelled to Wheeling. 



From Philadelphia to Wheeling, the Geologist has an 

 opportunity of observing almost every formation, from the 

 old primitive to the coal strata. On leaving Philadelphia, 

 the primitive soon disappears, and is replaced by the tran- 

 sition limestone, which is of a blue colour, very much in- 

 termixed with quartz in veins running through the mass. 

 There are also patches of white limestone which are ob- 

 served in sundry places, and which being of a highly crys- 

 talline character, might almost induce us to rank this lime- 

 stone as primitive. 



We find occasionally breaking through the limestone, 

 hills composed of amphibolic rocks ; this accident is more 

 frequent as we approach the Brandywine. These hills are 

 very readily discernible from the undulations of the lime- 

 stone country, by the difference in their outward form, 

 which in the limestone hills is mammillary, constituting 

 low and rounded swells ; while the amphibolic hills are 

 steep, and covered with a wilder vegetation. Beyond Lan- 

 caster the rocks assume a slaty appearance, which increased 

 as we approached the Susquehanna. At Columbia we had 

 an opportunity of observing the rock as it is laid bare in 

 the bed of the river. It there appears to be the red sandstone, 

 and is that mentioned by Mr. Maclure in his observations 

 on the geology of the United States. It constitutes part 

 of a red sandstone formation, which crosses through the 



