258 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



els id railroad and canal surveys, and has obtained data for the 

 heights of six thousand places, which give the levels of the 

 surface of the state at every point along the lines of survey. 

 The planes of reference have all been compared with each 

 other with great care, and all elevations reduced to Chicago 

 city datum, which is low water in Lake Michigan in 1847. 

 Contour lines for every fifty feet of elevation above Lake 

 Michigan have been drawn, and are represented upon the 

 maps accompanying the pamphlet, which presents a good 

 general picture of the surface configuration. These tortuous 

 lines, which to the casual observer may seem to be of little 

 interest or value, will be highly appreciated by every intelli- 

 gent person, and especially by those engaged in engineering 

 enterprises. From the map it appears that the lake shores are 

 depressed, the surface swelling geutly up toward the interior 

 regions: the rise beino- one or two hundred feet within a few 

 miles, and afterward much more gradual. A few bluffs and 

 steep shores are presented between Saginaw Bay and Lake 

 Huron ; but in general the steepest grades are found in the 

 eastern portions of the state. Along the border of Lake 

 Michigan stretches a series of sand dunes, or piles of fine 

 silicious sand, piled up by the easterly winds to a height of 

 one or two hundred feet. Back of these dunes the surface 

 is depressed, and frequently occupied by marshes and la- 

 goons. The average elevation of the interior of Lower 

 Michigan varies from four hundred to one thousand feet, 

 with many marks of the erosions that in post -geological 

 ages have pared down the original surface, and establish- 

 ed the existing slopes of the land and even the bottom of 

 the lake. Eighteen summits are enumerated by Professor 

 Winchell. They are usually gently undulating plateaus, 

 through which drainage valleys of moderate depth have 

 been excavated. In the northern peninsula, owing to the 

 want of accurate data, so minute a survey can not at pres- 

 ent be entered into. The highest summit on the Marquette 

 and Ontonagon is 1186 feet; while the hills north of Lake 

 Michigama are 1215 feet above that lake; and other points 

 near by reach 1250 feet. Beyond the Ontonagon River the 

 greatest altitude of the Porcupine Mountains is quoted at 

 1380 feet. Especial attention is called to the fact that the 

 longitudinal axes of the topographical and hydrographical 



