-1830] WRITINGS OF JOSEPH HENRY. 27 



the view on its southern side the diflPerent strata of rocks 

 which deeply interlay the surface of the country to the 

 south, and presents a geological section in this state, perhaps 

 not less interesting than that at Paris, London, or Rome. 



The lowest pass from the ocean into the St. Lawrence 

 basin throughout its whole extent, except the bed of the St. 

 Lawrence river, is through the valleys of the Hudson and 

 Mohawk rivers. The highest part of this pass is near the 

 Little Falls, and is elevated only 425 feet above the level of 

 tide water. 



The elevations of the lowest passes to the south, between 

 the waters of Lake Ontario and those of the Susquehanna 

 and the Allegany rivers, are given in tables Nos. 5, 6, 7, 8 

 and 9. The lowest of these is shown in table No. 7, where 

 the Seneca lake approaches to within 18 miles of the Che- 

 mung river, and is separated from it by an intervening ele- 

 vation of 443 feet above the lake, or 890 feet above the ocean. 

 The pass through which the Ohio canal is being directed is 

 395 feet above the level of the lake. But the lowest pass to 

 the south from any of the western lakes is that between the 

 Chicago, a small stream emptying into the southern end of 

 Lake Michigan, and the river Des Plaines, a branch of the 

 Illinois. The summit is here only 17 feet above Lake 

 Michigan, or about 617 feet above the ocean.* This is the 

 most surprising and important hydrographical feature of 

 our country; as, comparatively speaking, it here requires 

 but a slight effort of art to give a new outlet to the upper 

 lakes, and to divert a portion of the waters of Superior and 

 Michigan from their present channel of the St. Lawrence to 

 that of the Mississippi. Indeed, two of the plans reported 

 by the canal commissioners of the State of Illinois, are to 

 cut entirely through the barrier, and to supply the summit 

 of a canal through this pass with water directly from Lake 

 Michigan, 



From the elevations of the several notches in the height of 

 land that surround Lake Ontario, we may infer the curious 

 fact, that if a narrow barrier of sufficient height were to exist 



* Report of the Canal Commissioners of the state of Illinois, 1825. 



