244 J. W. GOLDTHWAIT- — ALG0^'QUI:N and IROQUOIS BEACHES 



A still more remarkable resemblance between the Iroquois and Algon- 

 quin planes is found when the tilt rates of the two are compared. It is 

 a matter of some convenience that the measurements available on the 

 Iroquois beach are so distributed that they afford the construction of a 

 set of isobases at 100-foot intervals, if we take for our zero the altitude 

 of the beach at its southernmost point, Hamilton (363 feet). This has 

 been done in figure 3. It is well recognized that the differential uplifts 

 which warped the Iroquois plane extended southward as far at least as 

 the head of that lake, at Hamilton, and an unknown distance bej^ond. 

 Hence, although we take a line through Hamilton (in the direction 22 

 degrees south of east) as a zero line, we must not forget that zero is not 

 a true measure of the amount of differential uplift at that place. It is 

 quite probable that the post-Iroquois uplift at Hamilton amounts to 

 15 or 20 feet. We may therefore call the line a '^zero plus" line, and the 

 others "100 plus,'' "300 plus,^' etcetera. Having done this (see plate 5), 

 we may examine the tilt rates between these isobases and compare them 

 with the tilt rates between corresponding isobases of the Algonquin plane 

 in the adjoining district. 



Table for the Comparison of Tilt Rates of the Iroquois and Algonquin Planes 



Portion of 



Iroquois plane. 



Algonquin plane. 



plane 

 represented 

 (isobases). 



Data. 



Tilt rate 



(feet per 



mile) 



Data. 



Tilt rate 



(feet per 



mile). 



to 100 



Hamilton (363 feet) to 

 Kingston road (459 

 feet), 42 miles. 



2 24 



Grand Bend (607 feet) 

 to Port Elgin (710 

 feet), 79 miles. 



1.30 



100 to 200 



Kingston road (459 feet) 

 to Quays (557 feet), 

 32 miles. 



3.06 



Port Elgin (710 feet) to 

 Owen Sound (74 8 feet); 

 and Holland Landing 

 (752 feet) to Ore (811 

 feet), 40 miles. 



2.43 



200 to 275 



Quays (557 feet) to 

 Trenton (632 feet), 

 18 miles. 



4.17 



Oro (811 feet) to Kirk- 

 field (883 feet), 18 

 miles. 



4.00 



The comparison shows in each case a somewhat steeper tilt for the Iro- 

 quis plane than for the Algonquin. This must be due in a measure to 

 the fact that the zero isobase for the Algonquin plane marks the real 

 limit of uplift, while the ^^zero plus" line for the Iroquois plane is prob- 

 ably a number of miles north of the true "hinge line." If we only know 

 how far south of Hamilj:on to move the "zero plus" line to put it in the 



