536 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



a large bowlder in Alum Creek bottoms, near South Woodbury, "the 

 extreme dimensions of which are 9 feet by 7J feet, showing 4^ feet above 

 the grovmd. In this bowlder hornblende predominates, and the feldspar is 

 flesh-colored, quartz being scarce, giving a rather dark color to the whole.' 

 The bowlders are usually much smaller than the one noted by Winchell, 

 the majority falling below 3 feet in greatest diameter. 



The striae observed in this district, so far as the moraine is distinct 

 from the others, are confined to a single occurrence, the one in the west 

 part of Delaware where the bearing is S. 8° E. It appears in the list of 

 stria3 given in the discussion of the main morainic system. 



OUTER BORDER PHENOMENA. 



The ice sheet apparently had at the time the Broadway moraine was 

 forming two main lines of escape for its waters, the Scioto and the Olen- 

 tangy valleys. Of these the Olentangy seems to have been the larger_ 

 There are beds of gravel and cobble at Delaware near the outer Ijorder of 

 the moraine which show vigorous drainage, while Avest of Delaware on the 

 Scioto there is a terrace cut in the till that filled the valley, but the terrace 

 is capped with a finer gravel than that on the Olentangy. In each valley 

 the bed of the glacial stream seems to have been 20 feet or more above the 

 present stream. The breadth of the terrace on the Olentangy is nearly 

 one-half mile, while that on the Scioto is less than one-fourth of a mile. 



North from Marysville, where the moraine crosses the tract lying 

 between Mill Creek and Blues Creek, it is bordered on the south by a 

 gravel plain, which is said to follow it eastward to Ostrander, but it was 

 examined only near the Union County Infirmary, north of Marysville. It 

 consists of a plain one-half mile or less in width, slightl}' lower than the till 

 tract south of it, and 20 to 30 feet or more below the moraine north of it. 

 It is underlain by gravel but has a rich, black, mucky soil. An occasional 

 low mound of gravel dots its surface. Its altitude by barometer is only 10 

 feet above the bridge on Mill Creek at Marysville, and it is probably less 

 than 20 feet above the creek at its nearest approach immediately west of 

 the Infirmary. Since this low gravel plain forms a direct connection 

 between the upper and lower portions of Mill Creek, it may possibly be 



