SCIENCE. 



[N. S. Vol. XVIII. No. 444. 



sylvauia geological map, to reduction of 

 vertical sections to a uniform scale and to 

 construction of ci'oss-sections. 



Having completed his theological course, 

 Lesley was licensed to preach in 1844 by 

 the Presbytery of Philadelphia and at once 

 went to Europe, where he made a pedes- 

 trian tour through France and Germany, 

 which he rounded out with a brief course 

 of study at the University of Halle. Re- 

 turning to America he undertook colport- 

 age work in northern Pennsylvania for the 

 American Tract Society, which he pursued 

 with characteristic energy and success for 

 two years. In December, 1846, Professor 

 Rogers asked him to come to Boston, where 

 for five months he prepared duplicates of 

 the state map and of the geological sec- 

 tions, which were to be deposited in the 

 State Capitol at Harrisburg. "Wliile in 

 Boston he received and accepted a call to 

 the pastorate of the. Congregational church 

 at Milton, Mass., where he remained until 

 1851. In this interval his views respect- 

 ing some theological , questions developed 

 along lines not ^iiolly acceptable to his 

 ministerial associates, so that at the end 

 of four years he resigned his charge, 

 abandoned the ministry and returned to 

 Philadelphia, where he began practice as 

 a consulting geologist. At once his ser- 

 vices were sought again by Professor Rog- 

 ers, who had obtained an appropriation for 

 piiblication of the final report, and for 

 more than a year he was engaged upon 

 revision for that report. 



Thenceforward for forty years his labor 

 was incessant; there seemed to be no limit 

 to his capacity for work. He was recog- 

 nized at once as the most competent of 

 geological experts and his time was fully 

 retained. Yet from 1855 to 1859 he was 

 secretary of the American Iron Associa- 

 tion, for which he published in 1859 a huge 

 volume, the 'American Manufacturers' 



Guide,' a remarkable compendium of 

 theory, practice and statistics, which even 

 now is of great value. For twenty-seven 

 years he was secretary and librarian of the 

 American Philosophical Society, rarely ab- 

 sent from meetings and seldom failing to 

 present a paper or to take part in the dis- 

 cussions. He made elaborate survej's of 

 the Cape Breton coal field, of the Pennsyl- 

 vania Coke region, of the Cumberland Val- 

 ley iron ores, of the Tennessee coal area, 

 of the North Carolina iron ores; while he 

 foiind abundance of time to learn several 

 languages and to prosecute special studies 

 in various departments of literature and 

 philosophy. In 1872 he was made pro- 

 fessor of geology and dean of the faculty 

 of science in the University of Pennsyl- 

 vania; but in 1878, owing to the pressure 

 of other duties, he resigned the deanship. 

 The Second Geological Survey of Pennsyl- 

 vania was authorized in 1874, and he was 

 placed in charge of the work. This post 

 he retained until 1893, when sudden and 

 complete failure of health compelled him 

 to relinquish it. He retired to Milton, 

 where he remained until his death. 



His labor was unremitting during the 

 twenty years of service upon this survey. 

 He read the report of every assistant and 

 prepared most of the admirable indices 

 which make those reports so available; in 

 many cases he drew the base for the maps 

 and sometimes even transferred the out- 

 crop lines from manuscript sent in by the 

 field assistants. He maintained that there 

 was no other way by which he could ac- 

 quire complete mastery of the facts con- 

 tained in the reports. He wrote long 

 prefaces to most of the volumes, discussing 

 the results, and in several eases he rewrote 

 reports that the matter might be presented 

 in a more systematic way. These prefaces 

 and editorial notes did not always seem to 

 the authors to be either necessary or val- 



