MARINE PLANE 241 



This shoreline of sealevel waters has been mapped at various points in 

 the Saint Lawrence Valley, In the Ontario basin and upper Saint 

 Lawrence it is represented by the Gilbert Gulf beaches, described in 1905 

 (117). The summit features of the marine shore are now traced in 

 practical continuity the whole length of both sides of the Hudson-Cham- 

 plain Valley, about the Covey Hill salient, and through the Saint Law- 

 rence-Ontario Valley until they pass beneath the waters of Lake Ontario 

 near Oswego (117, page 714). The remarkable series of heavy gravel 

 bars which lie at 525 feet above Covey Hill salient, passing near Covey 

 Hill Post- Office, and through Maritana and Franklin Center, reentering 

 New York at Boyds Lines, represents a relative pause in the rising of the 

 land. This beach series is over 200 feet below the summit plane of the 

 sealevel waters. West of Plattsburg this lower beach series disappears, 

 while the Cannon Corners, the summit series, is remarkably heavy, and 

 is represented by shore phenomena the whole length of the Champlain- 

 Hudson Valley, on both sides. On the north face of Covey Hill the sum- 

 mit marine plane is poorly represented, for the reason that the upper 

 slope had been swept bare by the heavy ice-border drainage of the doAvn- 

 draining Iroquois, so that little material was left on the slope for the 

 construction of bars, and because the work of the waves and currents on 

 the salient was erosional and not constructional. 



The Cannon Corners beaches are on extensive tracts of cobble delta 

 which were built in the sealevel waters by the latest outflow, around 

 Covey Hill, of the lowering Iroquois waters. This stretch of delta lies 

 along the east edge of a broad belt of bare Potsdam sandstone, the "Staf- 

 ford" and "Blackman" rocks, which were swept clean by the stream-flow. 

 The relation of the lowest distributary channels on these deltas to the 

 cobble beaches helps to determine the altitude of the standing water, 

 which is taken as 740 feet at the Cbvey channel. Because of the critical 

 relation of the marine plane to the latest level of Iroquois an isobase of 

 740 feet is drawn through the Covey outlet. The isobases of 600 and 

 700 feet are given theoretical positions, but in good accordance with 

 abundant data on both the New York and Vermont sides of the Cham- 

 plain Valley. 2 



No attempt is made to locate the 800-feet isobase, but this may be done 

 after examination of the marine summit in the north edge of Vermont. 

 It seems certain that the sealevel waters passed over the top of Mount 

 Royal, at Montreal. 



2 The detailed descriptions and mapping of the marine and Iroquois phenomena will 

 be given in publications of the New York State Museum and the Vermont Geological 

 Survey. 



