636 



GEOLOGICAL SURVEY OF THE TEERITOEIES. 



Elevation of Buffalo, Cleveland directrix, and mean surface of Lake Erie — Continued. 





Feet. 



Various datam-plpnes. 



Elevation in feet 

 above mean sur- 

 face of Atlantic 

 Ocean. 



Adopted result 







575. 68 



on pier.) 



Differences of the other results from the one adopted. 



- 1.04 



- 0.41 



















The first determination is adopted, because it is the result of many- 

 years' leveling over the Erie Canal, connected with Cleveland by a very- 

 favorable month of observations on the lake surface, and connected with 

 mean sea by the levels of the United States Coast Survey. 



The United States Coast-Survey line from their tide-gauge ati^ew York 

 to that at Albany was run for scientific purposes, and is undoubtedly 

 leveling of the first quality. The Erie Canal has been in process of con- 

 struction and enlargement for over fifty years. During this time the 

 levels must have been rerun many times, and the benches and compu- 

 tations checked by a succession of different engineers. Their final 

 report should be of the highest authority. The mean surface of Lake 

 Erie, during a month with light winds, when the fluctuations of the lake 

 were small, is considered a level plane for connecting the west end of the 

 canal with Cleveland. I think these reasons sufficient to justify me in 

 accepting the first determination as against those by' the railroad-lines. 



The result may then be considered as showing great accuracy in the 

 raih^oad surveys, which are from 480 to 600 miles long, and yet differ 

 but about one foot from the canal-levels. 



At Harrisburgh, where the lines of the second and fourth determinations 

 cross, the checking is very close. The height, as brought by the U. S. 

 C. S. and Pa. R. E. from Earitan Bay, one hundred and seventy -five 

 miles, is 319.91, while that brought from Baltimore by the N. C. E. E. 

 is 319.75 ; the two differing only J/^ of a foot. The elevation of this 

 same Market-street depot at Harrisburgh by the P. & E. E. E., reported to 

 me by the chief engineer May, 1874, is 308.03 above M. T. Philadelphia, 

 which would be 311.38 above M. T. Atlantic Ocean. This line is evi- 

 dently in error about 8 feet between Philadelphia and Harrisburgh, but 

 I believe it to be mostly in their computation, and not in the instru- 

 mental work. 



At Pittsburgh the Pa. E. E. is again checked by the B. & O. E. E., 

 which, in a number of reports, give the elevation of their depot as 735 

 feet above mean tide at Baltimore. By the report of the city-engineer, 

 the B. & O. E. E. depot track is 7.75 feet below that of the Union 

 depot ; hence the elevation of the track in the Union depot at Pitts- 

 burgh, by the B. & O. E. E. above M. T. Baltimore, is 742.75 feet. That 

 by the Pa. R. E. was 744.91 feet above M. T. Earitan Bay. As it is not 

 known to me how this mean tide was determined at Baltimore, nor is it 

 known whether mean tide at Baltimore is the same as the mean ocean-sur- 

 face, and as the B. & O. E. E. levels have not been subject to as many 

 revisions as those of the Pa. E. E., and the connection of the Pittsburgh 



