Madge — Notes on Preglacial Drainage in Michigan. 159 



is constructed with contour intervals of 100 feet, the contour 

 lines being arranged in harmony with the theory of a deep 

 central valley in the location above indicated. The valley cor- 

 responds to the 300-foot contour (above sea level), the lines 

 rising to the north and south. There is but a brief space to 

 the south between the 300-foot and 400-foot contours ; thence 

 to the 500-foot contour the distance is from five to ten miles, 

 and fifteen or twenty miles farther to the 600-foot line. The 

 600-foot line enters Ionia County near the northwest corner 

 and traverses the county in a southeasterly direction, crossing 

 Grand river a short distance east of Ionia City, at the locality 

 of the outcrop of Carboniferous sandstone, known locally as 

 the Ionia sandstone quarry. This outcrop in its bearing upon 

 another problem has been described more ,f ully in a previous 

 paper.* It is the only outcrop in this part of the state, is 

 located on the flat bottom of the river valley, and has an alti- 

 tude of about 650 feet, or fifty feet higher than the contour 

 line, which presumably is intended to represent the average 

 altitude of the rock surface in this vicinity. 



A comparison of this outcrop with some neighboring locali- 

 ties reveals some surprising irregularities. To the east the 

 rock surface is quite unknown, but at Lyons, three miles east, 

 a well has been sunk to a point a little below the 600-foot 

 level, and another at Pewamo, six miles farther east, nearly to 

 the 500-foot level, without penetrating rock. To the west, 

 however, more definite results have been attained. In the 

 city of Ionia, three miles down the river from the sandstone 

 outcrop, two deep wells were put down two years ago, pene- 

 trating rock at about the 550-foot level. As Ionia is located 

 between the 600-foot and 700-foot contour lines on the map, it 

 is seen that the 600-foot line must be removed several miles to 

 the southwest at this point. 



But this is not all. Nine miles still farther down the valley 

 the village of Saranac now has in process of construction a 

 well which at last reports was down to a depth of more than 

 250 feet, the rock surface having been found at a depth of 

 248 feet. The location of the well has an elevation of about 

 650 feet, hence the rock surface is at about the 400-foot level. 

 It follows that not only must the 600-foot contour line be 

 shifted so as to include this locality, but also the 500-foot line, 

 which appears on the map 25 miles to the north, while the 

 400-foot line would pass through Saranac instead of bordering 

 the central valley 30 to 40 miles away. That is, the rock sur- 

 face at Saranac is only about 100 feet above the bottom of the 

 central valley. 



* This Journal, November, 1895. 



