638 



GEOLOGICAL SURVEY OF THE TFEEITOEIES. 



ELEVATIONS OF LAKE HURON", ETC.— Continued. 



Surface of Lake Michigan, mean of twenty years — 



Alliance, by C. &P.E. R 



Alliance 



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

 W.SZ.C., 1872, report. 



Chicago depot, track P. F. "W. & C. R. R 



Chicago directrix, by city-engineers, 1872 



Chicago directrix 



Surface of Lake Michigan, mean of past twenty years 

 Chicago directrix, by P. F. W. <&. C. R. R., mean of Al- 

 liance and Crestline connection with Cleveland. 

 Surface of Lake Michigan 



Eighth determination. 



Cleveland directrix 



Cleveland, L. S. &. M. S. depot, by city-engineer , 



Chicago, L. S. & M. S. depot track, by profile procured 

 at the office of chief engineer, October, 1873. 



Chicago, L. S. & M. S. R. R. depot track 



Chicago directrix, by city-engineer, lb72 



Chicago directrix 



Surface of Lake Michigan, mean of past twenty years 



Ninth determination. 



Mean surface of Lake Erie 



Mean surface of river at Detroit, by State geological 



survey report. 

 Usual height of water in river on June 1 



Chicago depot of M. C. R. R., by M. C. R. R. report ... 



Chicago depot of M. C. R. R. & L C. R. R 



Chicago directrix, by chief engineer of I. C. R. R 



Chicago directrix 



Mean surface of Lake Michigan 



Final results. 



Surface of Lake Michigan and Lake Huron : 



(2) First detei'mination , 



(2) Second determination 



(2) Third determination 



(1) Fourtli determination , 



(1) Fifth determination , 



(1) Sixth determination 



(4) Seventh determination 



(4) Eighth determination 



(1) Ninth determination 



(The figures in parentheses indicate the relative 

 weights with which the difierent determinations 

 enter into the mean.) 



Adopted result. 



Mean of nine determinations 



Mean surface of Lake Michigan for past twenty years 



The extreme range among the nine results is 



(This amount does not exceed the known fluctua- 

 tions of the lakes.) 

 Chicago directrix : 



Seventh determination 



Eighth determination , ... 



Mean 



Result by subtracting 2 feet from adopted result for 

 mean surface of the lake. 



Adopted result. 



Chicago city-directrix 



The observations at Chicago make the city-directrix . 



Feet. 



507. 55 



487.7 



"'aso' 



8-50 

 16.6 



3.00 

 LOO 

 13.20 



6.5 



Huron .. 

 ...do ... 

 ...do ... 

 ...do... 

 ...do ... 

 Michigan 

 ... do ... 

 ...do... 

 Michigan 



4.21 



Various datnm-planes. 



Above Cleveland directrix, 



Below Alliance 



Below depot track , 



Above directrix 



Above Cleveland depot . 



Below track of L. S. & M. 

 S. depot. 



Above Lake Erie. 



Above mean surface of 



river. 

 Above river at Detroit, 



June 1, 1869. 



Below L C. & M. C. R. R. 

 depot. 



State of water unknown. 



do 



Mean surface 



do 



State of water unknown . 



do 



Mean surface 



do 



do 



Below mean surface of 

 Lake Michigan for past 

 twenty years. 



.SS' 



