Association of American Geologists and Naturalists. 147 



farther west, compiled by Dr. Owen, but when as in the long and com- 

 plicated Appalachian chain, almost innumerable anticlinal flexures of 

 various lengths and forms, throw the strata into nearly countless belts, 

 some of them of extreme narrowness, and which wind about in strictest 

 conformity to the topography, their delineation is much more difficult, 

 and an accurate and ample map basis, on which to lay them down, be- 

 comes of the first importance. Impressed with this conviction and re- 

 luctant to see the errors and distortions of the existing map of Pennsyl- 

 vania, falsify the more accurately drawn lines of the strata, furnished 

 by a seven years' laborious survey, I have with the aid of my assistants, 

 especially Messrs. Jackson, Henderson, Lesley, McKinley and Whelpley, 

 constructed a more accurate general map of the Appalachian mountains 

 of the state on a scale of two miles to the inch, upon which I am able 

 to depict every outcrop and every axis of importance. Though far 

 from possessing the precision of a thorough map, it is the only approx- 

 imately exact picture we yet have of any part of our great mountain 

 chain, so peculiar in the symmetry of its structure, so instructive as to the 

 close dependence of topographical features upon the hardness, thickness 

 and dip of the strata, and so interesting in a yet more scientific light, 

 as revealing the nature of the grand and wonderful movements through 

 Vi'hich the great flow of an ancient sea, rose and became wrinkled into 

 this stupendous zone of long parallel mountain crusts. 



Availing ourselves of some of the abundant materials for a detailed 

 geological map of the United States, my brother and myself have 

 constructed for our own convenience a general map of the strata, four- 

 teen feet by twelve feet, painted on canvas by R. Smith. It aims not 

 at minute accuracy, nor does it embrace all the narrow belts of the 

 Appalachian formations in their southeastern outcrops, each of the 

 great natural groups of the strata only being represented in this part 

 of the map. 



"While we thus see how much has been done towards tracing the 

 limits of each formation, we must remember that accurate mensuration 

 of the strata has also for most districts, been carefully attended to. 

 Having at an early stage of their researches, ascertained the order of 

 superposition of the stratified masses, and analyzed them, at least ap- 

 proximately, into groups and formations by aid of their organic re- 

 mains, and their well-marked lithological limits, the geologists in charge 

 of the various surveys have, while tracing the boundaries of each 

 stratum, been patiently estimating its variations of thickness and its 

 changes of aspect, texture, and composition. The labors of Emmons, 



