554 THE JOURNAL OF GEOLOGY. 
Hulls gap, Lake Passaic” began itsvexistences") Sincesthemceron 
the last epoch had then reached its maximum extension, the 
area of the lake was ata minimum. The lake seems to have 
remained at approximately the same level during the time when 
the moraine and the subaqueous overwash plain which borders 
it were formed. During this period of maximum level there 
were formed, in part at least, the high-level shore lines in the 
extra-morainic basin. To this stage belong the broad, sub- 
aqueous overwash plain extending from Chatham to Morris- 
town, and perhaps also the somewhat lower plains near West 
Summit, the gravel deposits near Bernardsville, Basking Ridge, 
Lyons, Millington, New Providence and New Vernon, as well as 
others of less importance. This stage of the lake may be called 
the Madison stage, from the fine development of the subaqueous 
overwash plain west of that place. During this period there 
were doubtless minor oscillations of the water level, due chiefly 
to varying rates of melting of the ice. Such oscillations of 
level may perhaps explain some of the minor inequalities in the 
heights of the different lobes of the subaqueous overwash plain. 
The retreat of the ice-——As the ice melted back from the 
moraine, the lake increased in area by successively filling those 
parts of the basin from which the glacier withdrew. During 
this period, the lake must have been more or less completely 
divided into two parts by the moraine, which, for part of its 
course across the basin, rises above the maximum water level. 
This barrier did much to prevent débris-bearing icebergs from 
reaching the extra-morainic basin, and thus limited the time, dur- 
ing which berg deposits could be made outside the moraine, to 
the period of ice advance. 
During the retreat of the ice, an embayment of several miles 
affected the front of the glacier, where it crossed the basin of 
the lake. The glacial deltas between Boonton and Parsippany, 
southeast of Boonton, north of Montville, at Jacksonville, 
Upper Preakness and Caldwell, were all formed by glacial 
streams while the ice edge was in the immediate neighborhood. 
The ice seems to have remained upon the higher ground above 
