MODIFJCATJOX OF Till: <;RK.\T LAKES 



243 



searching the rect)i-(ls I was able to seU^ct certain pairs of .slatiniis 

 at which the rehitive heights of pennaniMit ))()ints on the shore 

 (equivalent to A and B of the diagram) had hcen practically de- 

 termined twenty or more years ago. At some of these stations 

 gages are still read ; at others I establisht gagi's and nm the level- 

 ing lines necessary to connect them with tlie old benches. At 

 all of them observations were maintained from July to October, 

 1896, and these observations, in combination with the levelings, 

 afforded measurements that could be compared with those made 

 earlier so as to discover changes due to earth jnovement. 



It will not be necessary to give here the details of observiition 

 and computation, as they are fully set forth in a paper soon to 



5 ondusky 



FIG. 7 — MAP OF TUB GRliAT LAKES, SHOWING PAIRS OF GAGING STATIONS AND 

 ISOBASKS OF OUTLETS 



The isobases are markt bj' full lines. Broken lines show the pairs of stations 



be printed by the Geological Survey, but the general scope (.f tlie 

 work may be briefly outlined. As the tilting shown by the geo- 

 logic data was toward the south-southwest, stations were, so far as 

 possible, selected to test the question of motion in that direction. 

 The most easterly pair were Sacketts Harbor and Charlotte, New 

 York, connected by the water surface of F.ake Ontario (see map, 

 Fig. 7). From observations by the U. S. Lake Survey in 1S7I, 

 it appeared that a bench mark on the old light-house in Char- 

 lotte was then 18.531 feet above a certain point on the Masonic 

 Temple in Sacketts Harbor. In bSlX; the measurement wiis re- 



