No. 7.] WHITTLESEY — LEVELS OF LAKES. 413 



Eltvatloii of the Great Lalccs ahovc the Oceini. --^ 



It is uot practicable to fix the elevation of the surfaces of 

 these lakes, until their mean fluctuation is known. The results 

 I propose to give, are therefore only approximate. 



On Lake Superior the greatest known range of level is three 

 feet, with indications of a much greater range. Lake Ontario 

 has a variation of four feet, nine inches, well determined by 

 water registers, since the year 1812. 



The surveys of the Upper Lakes, by the Uuited States Gov- 

 ernment, now in progress, will eventually fix the mean level of 

 all the lakes, by observations which are made twice each day. 



For present use, I give the mean results of instrumental sur- 

 veys between tide water and the lakes, and between the different 

 lakes. 



Before doing this I must remark, that in none of them is the 

 stage of water noted, at the date of the Survey, whether above 

 or below the mean. There is therefore room for a plus or minus 

 error of two or three feet, when referred to a plane, which shall 

 be fixed upon, as the mean level of each lake. There is also 

 another ground of error. The lakes are not strictly level but 

 have an inclination or descent towards their outlets ; thouuli this 

 may be small, and in part corrected by the action of winds. 



To fix the elevation of the lakes, I begin at those nearest the 

 sea, to which instrumental surveys have been made. The Upper 

 Lakes are not thus connected by direct lines, but their height 

 above tide is determined by reference to those below. 



There is quite a discrepancy in the results, which can be ac- 

 counted for as I have above stated. 



LAKE ONTARIO. 



By lockage in the JSt, Lawrence canals, above mean tide, 234^ feet. 

 By canal surveys of New York, above mean tide, 232 " 



Mean elevation, 233i teet. 



* In a letter to the Editor, Col. Whittlesey states that this portion 

 of his paper was '» inserted in 1866 in a Report on a part of Minnesota,'' 

 and that the estimates ditl'er somewhat from those which have beeii 

 recently made by the U. S. Coast Survey. The importance of a 

 '< revision of the descent from Lake Ontario to Quebec" is also urged. 

 —Ed. 



