A RECONSTRUCTION OF WATER PLANES 473 



200 miles to the northeast of this region; for it had withdrawn from 

 the Mattawa valley, east of North Bay (see Fig. i), and at this distance 

 its attraction on the waters would hardly have raised the lake surface 

 more than an inch or two to the mile, according to Woodward's com- 

 putations. Furthermore, the water planes come together at a single 

 point. They should converge in turn to a series of points, feather 

 fashion, if they marked the attraction of the lake to successive posi- 

 tions of the retreating ice front (see Fig. 2). Evidently, then, the 

 inclined position of the planes, and their fan-like relation, must be 

 attributed to earth movements. 



The Hne from which the planes diverge (the "hinge line" on the 

 map, Fig. i), or as seen on the profile (Plate I) the point at which 

 they split, might be determined, it seems, in either of two ways. It 

 might mark the southern limit of a series of deformations, acting thus 

 as a hinge on which the tiltings took place. If so, it is evident that 

 here were no less than ten or fifteen distinct tilting or warping move- 

 ments, all of which hinged on the same line. On the other hand, the 

 point of splitting might be located at an outlet (or along the hne of 

 equal deformation through an outlet) , which together with the region 

 north of it had been raised by tiltings; for as the outlet rose, the 

 horizontal surface of the lake would rise, south of it, drowning the 

 old shore lines there, while to the north the former shore lines would 

 be raised out of water each time and would come to form a fan-like 

 series. This process is illustrated diagrammatically by Fig. 4. 



The choice between these two explanations for the case at hand 

 may be quickly made, if one considers the information shown on the 

 map (Fig. i). There are two outlets, only, which could possibly be 

 associated with the splitting, viz., the Kirkfield and the Port Huron 

 outlets. The isobase through the former (if it were drawn an 875- 

 foot line, parallel to the 835-foot isobase on the map) would pass 

 nowhere near Onekama, but rather through the upper peninsula 

 of Michigan. That is a district as yet not critically examined. The 

 Port Huron pass lies south of the "no tilt" line (or "hinge line" as 

 it is called in Fig. i) ; that is, it lies within the district which has been 

 unaffected by uplifts; consequently no fan-like splitting can occur 

 at it or in line with it. It seems necessary to conclude that Onekama 

 lies on the hinge line of the tiltings which raised all the planes into their 



