GAEDNEE.] GEOGEAPHY ELEVATION OF DATUM-POINTS. 



637 



depot is not known to be with tlie same grade given in the profiles of tlie 

 milroad, I consider the Pa. E. E. result as being the more reliable for 

 the present elevation of the track in the Union depot. 



The line of levels from Baltimore, by the N. C. K. E. to Harrisbnrgh, 

 and thence, by the P. & E. E. E. to Lake Erie, at Erie, a distance of four 

 hundred and twenty-six miles, reaches the lake with an error that does 

 not exceed 2 feet. 



ELEVATIONS OE LAKE HUROJf, LAKE MICHIGAIS^ AND THE CHICAGO DIRECTEIX. 





Eeet. 



Vaiious datum-planes. 



Elevation in feet 

 above moan sur- 

 face of Atlantic 

 Ocean. 



First determination. 



Lake Ontario at Oswego, by TJnited States Coast Sur- 

 vey and Erie Canal. 

 Surface of Georjiian Bav, Lalie Huron, at Collinc;- 







249. 99 



340. 00 



Above Lake Ontario 



■\vood, by N. E. R. of Canada. 



589. 99 



Second determination. 

 Sarface of Lake Huron at Sarnia, soutb end of lake, 



341. 00 



Above Lake Ontario 



by G. T. E. W. of Canada. 

 Surface of Lake Huron 





590. 99 



Third determination. 

 Mean surface of Lake Huron at Sarnia, by G. W. E. 



340. 00 



Above Lake Ontario 



W. of Canada. 





539. 99 

 573. 08 



Fourth determination. 



Mean surface of Late Erie, by United States Coast 



Survey and Erie Canal. 

 Surface of Detroit Eiver at Detroit, by State geologi- 







3.00 

 11.60 

 14.60 



Above Lake Erie 



cal survey report. 

 Mean Surface of Lake Huron, by G. W. E. W. of 



Above surface of river at 

 Detroit. 





Canada. 

 Difference of Lake.Erie and Lake Huron, mean sur- 





faces. 

 Mean surface of Lake Huron 





587. 68 



■ Fifth determination. 

 Surface of Detroit Eiver at Detroit, by State geologi- 



3.00 



.■55. 60 



43.00 

 12.6 



15.6 



Above Lake Erie 



cal survey report. 

 Junction of D. & M. E. E. and G. T. E. E., by D. & M. 



Above -water in Detroit 



Eiver, Sept. 24, 1868. 

 Below Milwaukee junction 

 Above river at IJetroit, 

 September 24, 1808. 





E.E. ^ 

 Surface of Lake Huron, by G. T. E. W. of Canada 





Lake Huron 





Do 





Surface of Lake Huron 





588 68 



Sixni, determination. 

 Surface of Detroit Eiver at Detroit 



3.00 

 10.74 



13.74 



Above Lake Erie 





Surface of Lake Michigan at Grand Haven, by D. 



Above liver at Detroit, 



September 24, ieC8. 

 Above Lake Erie 





& M. E. E. 

 Lake Micliiican 









586 S-"" 



Seventh determination. 

 Cleveland directrix 







575 68 



Crestline, b y C. C. C. & I. E. E 



577. 30 



Above Cleveland directrix. 





Crestline 





1 15-2 9B 



Chicago depot of P. F. W. & C. E. E. track, by P. E. 



W. & C. E. R. report, 1872. 

 Chicago, P. F. W. &, C. dtjpot track 



558. 



Bolow Crestline 







594 38 



Chicago city directrix, by city-eu'rineer, 1872 



8.5 



Below top of I'ail in P. E. 

 W. & C. depot. 





Chicago directrix , 



53.") 88 



Mean" suifacc, of Lake Michigan for past twenty 

 years, by city-engiucer'a report. 



2.00 



Above cily-dircctrix 









