2 



ence to, and Comparison with this, his fixed guide, that the 

 naturalist can discover his bearings. A like determination 

 is one of great importance, and we may say of absolute neces- 

 sity to the prosecution of any geological inquiry. Geological 

 levels are to the geologist as the compass to the mariner, and 

 we would here beg leave to call the attention of the society to 

 the attainment of this first and all-important object of research. 



The short time we spent in York county scarce enabled us 

 to commence an examination of this district, we humbly claim 

 the indulgence of the very learned gentlemen of the society for 

 the meagre gleanings we now offer. We have thought that the 

 collection of facts concerning rocks, minerals, their localities, 

 &c. might be useful in filling up some masterly and comprehen- 

 sive chain of observation. If we were all to throw down upon 

 paper the various rocks over which we pass in our different 

 perigrinations, but a short time would elapse before we could 

 present to the world a mass of information orderly embodied in 

 a geological map of the state of Pennsylvania or of the United 

 States of America. 



The county of York is bounded on the north and east by the 

 river Susquehanna and the county of Cumberland, on the west by 

 by Adams county, and on the south by the state of Maryland. 

 Indications of mineral deposits were here remarked at a very 

 early period in our history. Copper was foundby some of the 

 followers of William Penn in the township of Hellam, which 

 Was included in that portion of land set apart by him as his 

 mining tract. 



Two distinct ranges of mountains divide the county. The 

 South Mountain, which is a most important range, takes its 

 rise a little back of Diilstown, and continues on through Mary- 

 land, crossing the Potomac below Harper's Ferry ; the Cone- 

 wago hills are parallel, and have the appearance of belonging 

 to the same system. The Pigeon and Round Top hills do not 

 much deviate from an easterly and westerly direction. It is 

 from the summit of the last mentioned hills, that the observer 

 descries the distant and minor highlands, and can obtain a cor- 

 rect idea of the physical geography of this interesting district. 



