Dec, 1908.] Rock Terraces. 4°^ 



A magnificent rock terrace on the east side nearly one and 

 one-half miles long lies between the Columbus Fishing Club pond 

 on the north, and Fishinger's Bridge on the south. It narrows 

 toward the north, but attains a width of a fourth mile in its 

 central and southern parts. The terrace top averages about 

 70 feet above the river and has rehef of 20-30 feet. The highest 

 part is central, and the rock surface descends eastward as well as 

 westward, northward as well as southward. South of the central 

 higher part a depressed contour surrounds ten acres, and beyond 

 the depression near the private road occurs a true sink hole. A 

 little washed gravel is found on the terrace top, notably at the 

 south, but in no abundance. Soil on the terrace top is otherwise 

 thin, cherty alluvium. The terrace front is a continuous rock 

 bluff, sometimes precipitous. The bluff behind this terrace is all 

 of drift ; and the rock below the drift is lower than in the terrace 

 top, as is revealed by well records and by the absence of rock in 

 the ravine east and southeast of the terrace. One well east of 

 terrace goes almost 40 feet below the terrace before reaching 

 rock. A large alluvial pan of modified drift built upon the 

 terrace argues for its age. 



By wav of interpretation, it is suggested that before the last 

 ice sheet overspread this region there was a valley lying eastward 

 at this point from the present Scioto which had attained a depth 

 within 30 feet as great as the present valley; that this valley 

 became drift filled, and then the glacial drainage, and subse- 

 quently the present Scioto, took their course across the drift 

 plain. After cutting down for some time and sweeping off the 

 drift, the stream found itself on the rock of the terrace, a portion 

 of the western side and bottom of the filled valley. Instead of 

 sliding eastward into the old valley, the Scioto began dowa 

 cutting in the rock on the western side of its valley, and thus, 

 carved the present gorge 70 feet deep below the terrace top. It 

 has not been determined whether the sink hole mentioned, 

 belongs with the post-glacial drainage system or not, but it is 

 believed that it was formed before the last ice advance. 



The largest terrace of all lies on the east side of the Scioto, 

 begins about three-fourths mile down stream from the large 

 storage dam and continues down stream 21^9 miles or practically 

 to the big bend in the river, where it turns eastward around 

 Marble Cliff to receive the Olentangy. This terrace varies in 

 width from a few yards to about 300 yards. At its upper end, 

 it rises 25-30 feet above the river, but descends gently southward 

 to less than 20 feet above. Some of the terrace top slopes 

 toward the river, but north of Fifth Avenue a considerable area 

 is quite level and coincides with the rock structure, the bedding 

 planes, quite closely, and hence here might be called a structural 

 plain. In some places, the terrace top is well mantled with 



