Feb., 1907.] 



The Columbus Esker. 



69 



ridge has been eroded by a small branch of Neil's Run, which 

 crosses it just north of Sixteenth Avenue. 



A cross section (Figs. 3 and 4) at the northern end exposed 

 by the excavation for Woodruff Avenue shows it to be 128 feet 

 wide and 16 feet, 8 inches high. Here it rests directly upon the 

 bed rock, the Ohio Shale. The bottom layer of 12 inches con- 

 tains a great number of angular and partly water-worn pebbles 

 of the adjacent shale (Fig. 4). The strata of the large central 

 core dip outward from 20 ° to 45°. Here coarse and fine sand 

 alternate w'ith each other and with layers of coarse and fine 

 gravel. On either side at the edges the stratification is some- 

 what tumbled or disturbed. This is probably due to the melting 

 away of the ice at the sides and the subsequent settling of this 

 portion. The strata contain a few rounded pebbles of the Ohio 

 Shale and neighboring limestones, but the great majority are of 

 foreign rock. The sheet of till here caps these crumpled poi"- 

 tions and even runs over the entire form. 



At Eighteenth Avenue the curbstone of the street does not 

 reach the bed rock in the cut, but it was said to have been struck 

 some 4 or 5 feet deeper. The height of the esker above the curb 

 is 11 feet. As the ridge turns sharply to the southwest at this 

 point the exact width was hard to determine, but it was taken to 

 be 115 feet. The strata are deposited in a more uniform arch 

 over the center with less distortion on the edges. Deeper ex- 

 cavation, however, might show the edges to be distorted. The 

 strata consist of alternate coarse sand and fine graAxl. The whole 

 is capped by till. 





Fig. 5. A diagram to show the cross section on the north side of 

 Sixteenth Avenue, width 114 feet, height (exposed) 13 feet, 5 inches. 



The excavation for Sixteenth Avenue in the southern portion 

 did not reach the bed rock (Figs. 5 and 6). Here it rises 13 feet, 

 5 inches above the cut and spreads out laterally to a w4dth of 114 

 feet. The strata of the central portion are not laid clown in 

 such a uniform arch as those of the other two sections. Those 

 of the eastern portion dipping at an angle of 45°. Fine and 

 coarse sand and fine gravel alternate with each other. Water- 

 worn pebbles of shale were found ainongst those of foreign ma- 

 terial. A few of those of the latter material attained the size 

 of cobbles of 5 or 6 inches. Till covers the ridge as usual. 



