MEMOIR OF J. PETER LESLEY 533 



adjacent counties, confining his attention to the coal beds, while Mr 

 Hodge studied the iron ores. During this season he identified with the 

 Pittsburg the great coal bed at Salisbury, in Somerset county. In 1841, 

 the last year of the survey, he made a reconnaissance of the northern 

 and northwestern part of the state, studying the fourth and fifth bitu- 

 minuous coal basins as far south as Kittanning, on the Allegheny river, 

 and rounded out the year's work by a new study of the anthracite region, 

 completing the map left unfinished by Whelpley when he resigned, in 

 1839. During 1840 and 1841 Lesley worked out the. detailed and gen- 

 eralized sections of the lower productive and lower barren measures 

 now known as the Allegheny and Conemaugh formations — all this be- 

 fore reaching his twenty-second birthday. His studies were made when 

 much of the country was still a forest-covered wilderness, when roads 

 were few, when aneroid barometers and pocket levels were unknown, 

 and ordinary intervals were measured by estimate. His work in Somer- 

 set and the adjacent area was mere reconnaissance, yet his work, closely 

 reviewed by geologists of the second survey, needed little more of cor- 

 rection than did that of certainly one member of. the second survey 

 made in parts of that region thirty-five years later and under more favor- 

 able conditions. The skill with which Lesley and his youthful colleagues 

 unraveled complicated structure was little short of divination. 



The survey ended somewhat abruptly with the season of 1841 — the 

 geologists were scattered — but Professor Rogers began to prepare his final 

 report, hoping that the state might be induced to publish it. Lesley 

 had entered Princeton Theological Seminary to "indulge in a course of 

 theology," but his skill as topographer and draughtsman, his knowledge 

 of structure in all parts of the state, above all, his integrity and loyalty 

 made him indispensable to Rogers, so that all of the time, not impera- 

 tively required for study, was employed in preparing maps and diagrams 

 for the final report. At that time the only map of the state was so 

 inaccurate as to be undeserving of its name. There were numerous 

 county maps, some of which had been colored and in some measure 

 corrected by members of the corps; Lesley had made many corrections 

 wherever he went, and there were a few detached areas which had been 

 surveyed carefully. Such material as existed was given to Lesley that 

 he might construct the map. He has described the process, how the 

 county lines were forced into adjustment from both ends of the state to 

 the Susquehanna river, where the total error accumulated ; this gross 

 error was distributed backward east and west over the whole state " so 

 that the fundamental skeleton of the map was ' tempered ' like a piano 

 forte, being erroneous throughout, but with the local errors reduced to 

 a minimum." On this county line scheme he plotted the topography, 



LXIX— But.t,. Geol. Soc. Am., Vot,. 15, 190 



