TRIASSIC. 523 



limestones, and quartzites, as was the case along the northwestern border north of Flemmgton, 

 material from these formations has determined their local character. * * * 



The rocks of the Lockatong group overlie the Stockton beds conformably. They consist of 

 (a) carbonaceous shales, which spht readily along the bedding planes into thin laminae but 

 have no true slaty cleavage ; (b) hard massive black and bluish-purple argilhtes ; (c) dark-gray 

 and green flagstones ; {d) dark-red shales approaching a flagstone ; (e) and occasional thin layers 

 of highly calcareous shales. There are all gradations between these somewhat distinct tjrpes, 

 so that the varieties of individual beds are almost countless. Both ripple marks and mud 

 cracks occur at all horizons, showing that shallow-water conditions prevailed throughout the 

 time of their deposition. On the other hand, the absence of strong currents or violent shore 

 action is indicated by the extreme fineness of the material. 



********* 



In general the Brunswick group consists of a monfttonous succession of very soft argillaceous 

 red shales which crumble readily to minute fragments or split into thin flakes. Much of it is 

 porous, the minute, irregular-shaped cavities being often partially filled with a calcareous 

 powder. Oalcite veins and crystals are common in some layers. Locally lenticular masses 

 of green shale occur in the red. In size these range up to a foot or two in diameter, and vary 

 in shape from nearly spherical to lenticular masses, narrowing down to thin sheets along cracks. 

 They are undoubtedly due to chemical changes resulting in the leaching of the shale. 



Although the majority of this series are soft red shales, there are some hard layers, chiefly 

 near the base, and occasional beds of fine-grained sandstone and flagstones, some of which 

 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 raindrop 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. 



** ******* 



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 characteristics and merge along the strike into coarse sandstones and 

 massive conglomerates. This change is most striking in the case of the Brunswick and tlie 

 Lockatong groups, where red shales or black argillites change to sandstones and then into con- 

 glomerates, the pebbles of which are frequently 6 or 8 inches in diameter. Under these condi- 

 tions it is impossible to differentiate and limit these groups in this part of the field. 



**** * **** 



Important changes are found to occur as the beds are traced along the strike northeastward 



into New York. The Stockton beds disappear beneath the later deposits a few miles east of 



Princeton. 



**** * **** 



The Stockton beds certainly persist into New York, but the typical coarse arkose sand- 

 stone beds apparently thin out, and north of Nyack the group can not be identified with any 

 degree of certainty. The trend of the strata apparently carries the beds of this subdivision 

 beneath the Hudson River. 



Northeast of Princeton the outcrop of the typical Lockatong group grows narrower and 

 the thickness is less. Either the rate of deposition was slower to the northeast during the time 

 represented by the Lockatong beds elsewhere, and therefore they are thinner here, or else, the 

 rate of deposition being the same as elsewhere, the conditions favoring the deposition of black 

 argillite and shale did not last so long to the northeast of Princeton as nearer the Delaware. A 

 few miles northeast of Princeton the Lockatong beds also are covered by the Cretaceous deposits, 

 but they have been traced by borings as far as the Raritan River. They do not, however, appear 

 in the region west of the PaUsades and north of Newark. 



