234 J. W. GOLDTHWAIT ALGONQFIX AND IROQUOIS BEACHES 



out from maps whose scales range from 1 :400,000 to 1 :250,000. Plate 5, 

 prepared from a much smaller map, is intended merely to show the 

 broader features of warping, not to serve as a basis for estimating minute 

 details. 



Over the northern, or, more accurately, the northeastern, part of the 

 Michigan-Huron basins the Algonquin beach has been upwarped so that 

 it now slants southward at a rate that decreases down the slope of the 

 plane. The inclination ranges from about 5 feet per mile in the north 

 to 3 feet, 2 feet, 1 foot and less toward the south, to where the beach 

 actually becomes horizontal, over the southern half of Lake Michigan. 



The directions and rates of tilt in different districts, worked out after 

 all available wye-level measurements had been plotted on large-scale 

 maps, are tabulated in detail on page 235. 



These figures have been tabulated again, in a more compact form, for 

 the sake of comparison of tilt rates at corresponding altitudes in the dif- 

 ferent districts. 



Tilt Rates of the Algonquin Beach arranged for Purposes of Comparison. 



District. 



Tilt rates, in feet per mile, between successive 



isobases. 





0-50 



50-100 



100-150 



150-200 



200-250 



250-300 



Lake Michigan and Straits 

 of Mackinac 



1.16 

 0.75 



1.02 



1.82 

 2.22 



2.10 



2.85 



8.88 



8.40 





West side of Lake Huron . . . 





East side of Lake Huron 

 and south side of Georgian 

 Bav 



2.11 









Lake Simcoe district 



2.68 

 8 09 



8.00 

 8 20 



6 00 





' 



2.48 





■Average tilt rates 



0.97 2.05 



6.00 











Not a small part of the discrepancies between tilt rates in the same 

 vertical column in this table may be due to the necessity of taking sta- 

 tions which do not lie exactly on the isobases, and whose differences of 

 altitude are consequently not 50 feet, but range from 32 feet to 71 feet. 

 Detailed isobase maps drawn on a large scale show that the tilt rate is 

 more uniform between isobases than one might at first suppose from the 



