0)60 NEW YORK STATE MUSEUM 



SUMMARY OF GLACIAL HISTORY. 



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From wlmt has been stated of this district, it appears that rela- 

 tively early ii» the Glacial period the area now forining the western 

 |»art of Long Island received a thick coating of gravels and sands, 

 some of the del)ris being eroded from the deposits of the coast plain 

 remaining in the area, some of them being borne from the main- 

 land on the north ; that ])robably somewhere near the middle of this 

 time, as indicated l)y the occurrence of the deposits in the section, 

 there was an actual invasion of the district by ice, either floating ice 

 ur land ice, in either case probably the margin or detached floating 

 portions of the front of an ice sheet laying down till in the district. 

 These deposits as a whole underlie the moraines and are apparently 

 the Columbia formation of McGee. Certain aspects of the deposits 

 seem to be paralleled in Xew Jersey by the yellow gravel forma- 

 tions described by Salisbury.* Subsequent to their deposition, which 

 locally affords no decisive evidence of the relation of land to sea- 

 level, they appear to have been somewhat dissected by open air 

 streams, indicating an epoch of deglaciation or ice retreat of indeli- 

 nite duration. Following this came the deposition of two lines of 

 moraines in the area, an outer and inner or earlier and later, but in 

 the western part of the field the later ice front depassed the position 

 of the earlier advance. The land appears to have been as high 

 above sealevel as it is now, if not higher; and during the retreat of 

 the ice one or more temporary lakes existed back of the moraine, 

 flrst at 80 feet above the present sealevel, then possibly at about 40 

 feet. This lower body of water may have been at sealevel as 

 stated above. With the retreat of the ice front across East river, 

 the region escai)ed from the fleld of glacial action, and its latest 

 glacial deposits and features pertain to the very beginnings of the 

 ice retreat, a time but slightly past the culminating phase of the 

 last or Wisconsin glacial epoch. Of any such distinctions as a Cham- 

 2»lain and Terrace epoch there appears here no trace, for the over- 

 wash plain was making while the ice was at its maximum extension, 

 and tho irlaoial tfrraoos marked by the small deltas described in this 



'Salisbury, H. I). N. J. geol, sur. An. rep't state geol. 189o. p, 67-72. 



