THE NEWARK ROCKS 27 



afford valuable building material. Massive conglomerates along 

 the northwestern border are in part the shoreward correlatives 

 of the red shales. 



Evidence that the shales were deposited in shallow water is 

 abundant. Ripple-marks, mud -cracks and rain-drop impressions 

 occur at many horizons. In some quarries imprints of leaves, 

 of tree stems, or the stems themselves are frequently found. 

 The numerous reptile tracks which have made the Newark beds 

 famous occur chiefly in this subdivision. Typical exposures 

 occur along the Raritan River, particularly near New Brunswick. 

 The Brunswick beds are easily disintegrated and the fineness of 

 the residuary material renders its transportation easy. Conse- 

 quently the region underlain by these shales forms a lowland of 

 faint relief, much of which has an elevation of only 100 to 200 

 feet above sea level. This plain is best developed in the drain- 

 age basin of the Raritan River, from New Brunswick northwest- 

 ward to Flemington and White House. These rocks form also 

 the western and lower part of the Hunterdon plateau in the 

 vicinity of Frenchtown. 



Owing to two great faults these three subdivisions each occur 

 in three belts in the western part of New Jersey as shown by 

 Fig. 2. 



Litlwlogical changes in these types. — Important lithological 

 changes occur in all these beds as they are traced along their 

 strike. As the northwestern border of the formation is approached, 

 near Pittstown, the subdivisions lose their distinctive character- 

 istics and merge along the strike into coarse sandstones and mas- 

 sive conglomerates. This change is most striking in the case of 

 the Brunswick and the Lockatong groups, where red shales or 

 black argillites change to sandstones and then into conglom- 

 erates, the pebbles of which are frequently six or eight inches 

 in diameter. Under these conditions it is impossible to differ- 

 entiate and limit these groups in this part of the field. Before 

 considering these border conglomerates more fully, other modi- 

 fications in the beds will be noted. 



Important changes are found to occur as the beds are traced 



