474 



JAMES WALTER GOLDTHWAIT 



inclined positions. That so many tiltings, separated no doubt by 

 considerable intervals of time, should have had the same hinge suggests 

 that this line, for reasons unknown, is one of structural weakness. 



In order to show the significance of the fan-like profile of water 

 planes, in Plate I the following series of diagrams (Fig. 5) is introduced. 

 These present in a very conventional and much simplified way the 

 relation which the successive planes of Lake Algonquin and the 

 Nipissing Great Lakes should bear to each other according to 

 the present generally accepted interpretation of the history of the 

 great Lakes, worked out by Mr. Taylor. Since that history is 



X 



c 



b. 



G.-.. »--r;'.v... ............ ............ yr » d 



Fig. 4. — Diagram showing in profile how a fan-Hke group of water planes might 

 be produced by a number of differential uplifts which tilted a lake basin and its outlet. 

 Outlet at O. Uplifts affect region to the right of X. Three stages are shown. First 

 stage, outlet at i; horizontal water plane of the lake at aa. Second stage, tilting on 

 right side of X has raised outlet to 2; water plane aa has been inclined to aa^; the lake 

 has risen to plane hb, drowning that part of it which lies on left side of outlet. Third 

 stage, another uplift has raised outlet to 3; has tilted bb to bb"^, and increased tilt of a«i 

 to aa^; lake has risen to cc; on left side of outlet planes a and b have been drowned; 

 on right side, they rise, splitting at outlet, fan-fashion. 



recognized as subject to revision, through further study, the dia- 

 grams should be taken to represent simply the conditions which seem 

 most probable, in the hght of the evidence already at hand. Although 

 in the actual case the planes have been warped to curved profiles, 

 as shown in Plate I, they are represented in the diagrams as simply 

 tilted. This is wholly for the sake of simphcity, and must not be 

 thought to imply that the crustal movements were actually tiltings 

 instead of warpings. 



The final diagram (6, in Fig. 5) shows the present position of 

 these planes. That portion which lies south of the Trent outlet 

 is based on recent detailed work in the Michigan and Huron basins, 

 including that described in this* paper. The large profile, Plate I, 



