18 ON THE FRESH-WATER GLACIAL DRIFT 



shore line, the highest being 680 feet above its surface or 912 above tide. Prof. 

 Hall has described five of them on the New York side of the lake, the highest 

 being 762 feet above Lake Ontario or 1090 above tide. In Ohio I have noticed 

 but four regular and continuous ridges. There must have been others at lovs^er 

 levels now carried away by the advance of the shore line. In Michigan, they have 

 been noticed within thirty feet of the lake level. 



The first or nearest one to the lake is the most regular. I have its elevation at 

 or near the base, at twelve points along a line of seventy miles from the Conneaut 

 to the Black river. The height varies from sixty to one hundred and five feet. 

 It is very regular and continuous, and used most of the distance as a public high- 

 way, ready formed by nature for the use of man. Its height above the base varies 

 from fifteen to twenty feet. 



Occasionally the summit of the ridge is broken into sand knoUs of about the 

 same height, which may be seen at Painesville, Cleveland, and Avon. The lowest 

 summit of the ridge is eighty-five feet, and the highest one hundred and forty-five, 

 showing a difference of level longitudinally of sixty feet. This corresponds with 

 one in Washtenaw county, Michigan, which is about 140 feet above the lake. 

 Terraces due to an ancient shore line should be at the base nearly level. The 

 country on all sides slopes gradually toward the lake, so that the interior ridges 

 overlook those between them and the water. All the rivers and streams of the 

 region cut the ridges and the drift clay, frequently down to the rock below. 



Between the ridges where they are within a short distance of each other, there 

 are long narrow swamps which drain laterally into the streams. The height of the 

 second ridge in Ohio varies from 122 to 168 feet in a distance of 60 miles, the 

 greatest difference of level being 46 feet. The third and the fourth ridges are not 

 so well defined. 



Some points on the fourth ridge between the Cuyahoga and the Black rivers, 

 have an elevation of 173 to 203 feet. Around the west end of Lake Erie and on 

 the Canada side, they have been observed, but their altitude is not known. Like 

 submarine bars now forming, these have branches and spits, which sometimes run 

 across obliquely connecting two parallel ridges. Ancient lake ridges must not be 

 confounded with " lake beaches" which were formed afterwards, by the action of 

 the waves upon the shingle of the shore. 



On the north shore of Lake Michigan, there are remains of such beaches, com- 

 posed of gravel, and others around the south end of the lake composed of sand, 

 which are quite ancient, considered with reference to historical epochs, but which 

 belong to the alluvium. The surface of all the lakes has settled away, and is now 

 settling away in a very gradual manner, by the wearing down of their outlets. 



Beaches of water-washed sand, and shingle, as perfect as those now forming, are 

 seen rising in succession behind each other ; on Lake Michigan as high as eighteen 

 and twenty feet. There are in some places four of them within fifteen or twenty 

 rods of the present water-line. A more extended reference to this class of ridges 

 may be seen in Foster and Whitney's Keport on the Geology of Lake Superior, 

 Volume 2, Chapter 16. 



On Lake Superior the recent beaches are composed principally of sand. They 



