PORTION OF THE SCHUYLKILL COAL-FIELD. 89 



and, in like manner, the geologist, or the geological draftsman, or 

 the modeller, has to exercise his art, in putting together and ex- 

 hibiting in correct forms, the details he has labored so hard to 

 coUect. Above all things, let him avoid distortions in drawing. 

 It is incumbent upon those who undertake to enlighten and in- 

 struct others by diagrams, to exhibit those diagrams in true, and 

 not in false proportions. The master can no more hope to con- 

 vey to his pupil a right idea of a cube or a square, for instance, 

 by representing in his diagram its height four or five times its 

 breadth, than can the draftsman in our science, expect to convey 

 correct notions of geological arrangement by a similarly defective 

 process. 



Returning to the model before us. The local elevations above 

 the level of tide, have been ascertained at a sufficient number of 

 points, particularly in the coal districts, to convey the prevailing 

 characters of the country. A number of these heights, are marked 

 on their proper sites upon the model. All of these were found 

 by spirit level and positive admeasurements. The Pennsylvania 

 canal on the east bank of the Susquehanna river, where it cuts 

 through the second mountain, is three hundred and twenty-seven 

 feet above tide level in Chesapeake Bay. The Swatara river, 

 above Pinegrove, passes through the same mountain, tlurty-one 

 miles to the eastward, at the height of six hundred and nine feet 

 above tide. The prevailing elevation of the ridges which form 

 the north and soLith edges of the southern coal basin, is sixteen 

 hundred or sixteen hundred and fifty feet above tide water. As 

 a general remark, when casting a glance over the area here repre- 

 sented, we cannot but be struck with the comparative uniformity 

 in their elevations, and the extensive maintenance of those levels 

 along the crests of the ridges, when not broken by transverse 

 fissures. The Blue or Kittatinny Mountain, the southernmost 

 of these nearly parallel ranges, is probably the highest. The 

 coal range is next in elevation, and there is some lofty ground, 

 forming Short Mountain, between Peter's and Berry's mountain. 



Geolog-ical Features. — Under this head we shall here be very 

 brief; because that subject is not the primary object of this ad- 

 chess ; and because the region has received, or will receive, ample 

 7 



