PHILOSOPHICAL SOCIETY OF WASHINGTON. 23 



TSth MiCETiNa. Decembee 19, ISIl. 



The President in tlie Chair. 

 Forty-three members and visitors present. 



Mr. J. T. Gardner gave an extended abstract of a paper, 

 prepared by him for the Report of the Geological Survey of the 

 Territories for 18T3, 



on the use of RAILROAD LEVELUNGS IN DETERMINING ELEVA- 

 TIONS ON THE GREAT LAKES AND RIVERS IN THE UNITED STATES 

 AND IN THE ROCKY MOUNTAINS. 



(abstract.) 



In connection with the work of the Geological and Geographi- 

 cal Survey of the Territories under Prof. Hayden, Mr. Jas.^ T. 

 Gardner, the geographer of the survey, has undertaken to review 

 the evidence upon which rests the received elevations of the 

 principal points in the United States. The results are published 

 in the Report of Prof. Hayden for 1873. 



Mr. Gardner had before him over 1200 railroad and canal 

 profiles, collected in Washington by different departments of the 

 government. He also visited the offices of the leading railroads 

 to examine original notes and ascertain exact details at the 

 termini and intersection of roads, so that the profiles of the 

 -different lines might be accurately corrected. 



It was found that the old elevations given by our best au- 

 thorities had two leading sources of error. The eastern ends 

 of main railroads and canals had never been properly connected 

 with tide gauges, so placed as to give the mean level of the 

 ocean; and the old reports of railroad and canal heights had 

 in many cases been superseded by recent and more accurate 

 levellings. Having sifted his great mass of data to retain only 

 the most trustworthy of the lines, and carefully connecting these 

 with tlie U. S. Coast Survey tide gauges, Mr. Gardner proceeded 

 to determine the elevations of onr principal railroad centres from 

 ■as many independent lines as possible. 



At Cleveland there were three results, which only differed 

 among themselves one foot; and the five separate results for the 

 surface of Lake Erie differ only 2^ feet. 



The elevations of Lakes Huron" and Michigan are determined 

 by nine wholly or partially independent lines, which differ only 

 four feet. This agreement of results places the elevations of our 

 lakes bevond doubt. 



Lake Erie's mean surface is 573 OS feet, and Lakes Michigan 

 :and Huron are 589.15 feel above the sea. In the same way 



