A RECONSTRUCTION OF WATER PLANES 



469 



about 50 on beaches or benches that are less distinct, though not to 

 be neglected in a fair consideration of evidence. A distinctive symbol 

 is used for the two contrasted types of topography, benches and 

 beaches ; and the symbol for a well-formed beach or bench is different 

 from the one for a beach or bench that is faint. The size of the spot 

 is intended to cover the probable range of error in measurement. 

 The height of a cut bluff is shown by a wriggling vertical line. 



Fig. 3. — Map of the north end of Lake Michigan, showing the warped attitude 

 of the Algonquin water plane. 



Through the highest beach thus recorded a line or band was drawn 

 with a thickness (according to the scale) of 6 feet, to represent the 

 range of variation in height to be expected in the original construction 

 of the beach or bench. The line or band, when drawn as a gentle 

 curve, so as to pass most directly through the highest ordinates, in- 

 cludes 21 out of 24 of them. Of the 3 which are either too high or 

 too low, to fall within it, one at Carp Lake, fully 8 feet too low, is 



