IN TUE NORTH AMERICAN LAKES. 



FOR LAKE SUPERIOR. 



on the Mitre Sill, head of Canal, Sault St. M.uj. 



are less affected by winds and curi-ents, and the irregularities that arise from 

 indentations of the coast. Whoever undertakes to compare observations made at 

 the Sault St. Mary's, at Detroit, Buffalo, Niagara, and Ogdensburg, which are 

 situated upon straits or outlets, will at once perceive that the range of fluctuation 

 is o-reater than it is at Eagle river, Cleveland and Oswego, situated on the open 

 water. There is between them a correspondence, but, from causes that are appa- 

 rent, the changes of level at the same time may be greater or may be less upon 

 the St. Lawrence, the Detroit, or the St. Mary's rivers than upon Lake Ontario, 

 Lake Huron, or Lake Superior. 



If the width of the Detroit river at Fort Gratiot is greater than it is at Detroit, 

 a rise of a given number of feet in Lake Huron must result in a greater rise at 

 Detroit, the channel being narrower and more compressed. This is known to be 

 the case in the Niagara river. 



Below the falls for many miles is a narrow gorge where the river is compressed 

 into much narrower limits than it has at Black llock, where Lake Erie discharges 

 itself Wliile this Lake varies secularly, not to exceed six feet, the rise and fall 

 in the gorge below the suspension bridge is reported to be fifteen and even twenty 

 feet. But on Lake Erie and Lake Superior the best zero or line of reference is 

 furnished by the guard locks of the Erie and the Sault St. Mary's canals, and 

 althouo-h the position is not favorable in other respects, the zero is so convenient 

 and well established that I have reduced all the registers for these Lakes to the 

 same expression as those at the canals just named. 



In June, 1855, soon after the completion of the canal at the Sault, connecting 

 Lake Huron and Lake Superior, Ui: John Burt, the superintendent, caused his 

 assistants, INIessrs. Wm. Finney and M. B. Sherwood, to keep a register of the 

 depth of water at the upper and at the lower locks. These have been kindly 

 furnished me as late as the fall of 185G. They were not nia.le daily but fre(iuently 



