Davis and Wood.] 
422 
[Nov. 20, 
bay, and long sand bars or “beaches” have been built by the waves 
off shore. 1 The previous greater depression, by which the Yellow 
Gravel 2 or Columbia formation 3 was deposited and from which the 
land has recovered, has left small geographic record ; gravelly del- 
tas were formed at the mouths of the larger rivers ; terraces and bars 
were left along the shore line ; and stones and gravel, sometimes 
twenty or more feet thick, were spread over the submerged part 
of the Central plain and Southern lowland : for further account 
of which the student should refer to McGee’s papers already often 
quoted. 
40. Effect of the Glacial Invasion. Brief mention may be made 
of the numerous lakes within the glaciated area ; of the mounds 
and ponds along the morainic belt ; of the drowned lands along 
manjr streams ; of the occasional changes in stream courses due to 
drift barriers ; and of the washed drift that spreads over many ex- 
tra-morainic valleys ; but the reader can refer to the annual re- 
ports of the New Jersey survey for detailed information on these 
headings. 4 The temporary glacial lake within the Watchung cres- 
cent 5 also calls for mention, as its deltas and shore lines are del- 
icate geographic features of to-day. € 
The most considerable change of river course by drift barrier is 
that of the Passaic already mentioned. The heavy morainic ridge 
from Morristown to Chatham stands athwart the pre-glacial val- 
ley ; Great swamp now lies behind or south of this barrier, and 
the Passaic makes its escape by a roundabout course to the east. 
The Rockaway is also deflected from its ancient course by the mo- 
raine at Denville ; it turns northward over a divide between two lat- 
eral valleys, and descends rapidly over rocky reefs past Boonton 
on its new course. Many other examples will in time be de- 
scribed. 
41. Review. The details with which an essay of this character 
is necessarily encumbered make the clear presentation of its theme 
a difficult matter. The effort to shorten what is necessarily so 
long gives at times more definiteness of statement than is desira- 
ble in subjects that are still wide open to discussion ; but certain 
facts appear to stand out clearly enough. The Highland plateau 
is an elevated and faintly tilted peneplain of denudation, dissected 
1 Geol. N. J., ]885, 72. 2 Merrill, Geol. N. J., 1886, 129. 3 McGee, l. c., 367. 
4 Especially in the Reports for 1880, 14; 1884, 112. 
6 Annual Report, 1880, 63, with map in frontispiece. 
