SURFACE FOR^fATIONS OF SOUTITFRN NEW JERSEY. 487 



Dnrinc: its deposition tlie Triassic shale seems to liave made no eontiibntion to 

 the i^atlieriny; formation. Tlie stony material of tJie Jamesbur<i: is for the most 

 part snoh as eonld have been derived from tiie l*ensauken beds. None of the de- 

 composed materials of the Pensauken, however, entered into the composition of 

 the .lamesburg. Such trnmitic and gneissic materials, as well as such Triassic shale 

 and san<lstone of the Pensiiuken as ciime within reach of the waters which depos- 

 ited the .lamesburg, were so thoroughly disrupted that their identity was lost. 



TorocRArnir fkatirks a.\i> their history 



The toi>ography which was developed as the n^sult of the submergence which 

 made the .lamesburg formation is i)eculiar. It is a toi)ography which resulted from 

 the temporary submergence of an erosion surface developed in incoherent materials. 

 In some cases tlei)osits were made by currents running across the shallow pre- 

 Jamesburg valleys in such wise as to divide them into a series of isolated or semi- 

 isolated hollows. In many instances. these hollows are now occupied by ponds 

 and mai*shes. The marshiness which prevails along streams in nuich of central 

 ami southern New Jersey is believed to be due to the deposits which were made 

 during this time. Subse(]uent erosion has been insutticient to remove the obstruc- 

 tions then developed. The average depth of the Jamesburg formation is perhaps 

 not more than 10 feet, though it sometimes reaches 30 feet. 



Elevation followed the submergence and the Jamesburg formation was brought 

 above the water. The emergence was cither slight or recent, for drainage has 

 made but little headway in the establishment of new valleys and in the removal of 

 the obstructions de[)osited in the old ones during the Jamesburg depression. 



RELATIOS TO THE TRESTOX GRAVEL 



Subsequently the Trenton gravels were deposited in the Delaware valley by the 

 glacial waters of the last ice epoch which affected New Jersey. How far the James- 

 burg loam and the Trenton gravel are separated in time is undetermined. It is 

 probable that they are sutliciently distinct to be referred to dilferent epochs. In 

 origin they were certainly diverse, even if the interval between them was not long. 



Tnic COASTAL Terrace 



In the eastern part of the state, from Raritan bay eastward and southward, there 

 is a low and rather ill defmed coastal terrace, with an average elevation of about 

 45 feet, which is very nuich younger than the body of the Jamesburg forma- 

 tion. It is not known, however, to be separated from this formation by any con- 

 siderable interval of time. It is pcjssible that it represents no more than a halting 

 stage in the eniergence of the land after the deposition of the more wide sprea«l 

 Jamesburg. It is possible that it is to be connected in time with the Trenton gravels 

 of the Delaware valley. This is a matter for future determination. Even if it 

 marks no more than a temi)orary level of the sea during the emergence of the land 

 afti^-r the Jamesburg deposition, it nevertheless represents a distinct stag(» in the 

 history of the land surface, and as such demands recognition. 



Conclusions 



Little can now be allirnuHl concerning the relation of these several snlxlivisions 

 of the " yellow gravel " to formations which liavt- heretofore been recou'iiized. The 

 l,XL\-Hii.i.. (ivm.. Hor. Am.. Vor.. fi, 1804. 



