366 Leverett — Weathering and Erosion as Time Measures. 



Equivalents of Kansan or Pre-Kansan in the Labrador Field. 



The writer lias never had opportunity to study, or even to 

 travel across, the area in New jersey and northeastern Penn- 

 sylvania occupied by the sheet of old drift of the Labrador 

 field to which Chamberlin and Salisbury have applied the term 

 Jersey an. The patchy distribution and weathered appearance 



Fig. 7. 



Fig. 7. Part of Oelwein, Iowa, topographic sheet showing topography of a 

 so-called Iowan drift plain. The amount of erosion here displayed should 

 be compared with that in the Illinoian, figs. 3 and 4, and Kansan drift, iigs. 

 5 and 6. Scale, 1 : 173000. Contour interval, 20 feet. 



reported by those who have studied it, seem to indicate an age 

 as great as that of any drift sheet in the Keewatin field. It is, 

 therefore, considered by these students a probable correlative 

 of the Pre-Kansan or Sub-Aftonian drift of the Keewatin field. 

 The old drift of northwestern Pennsylvania, which has been 

 examined by the present writer, is thought from the weather- 



