158 AXXALS NEW YORK ACADEMY OF SCIE^-CES 



of Triassic time in this immediate neighborhood. The strata lying be^ 

 tween the Lockatong exposures and the nearest visible diabase sill show^ 

 however, only occasional horizons of unusual hardness ; the}^ are not as a 

 whole much indurated. It further appears that the silica cement was not 

 generally distributed in the vicinity of the diabase sill; and buried in- 

 trusives beneath the Lockatong are improbable. For these reasons, the 

 writer favors the idea of cementation after deposition, but independently 

 of the igneous intrusions. 



This siliceous cement is evidently a widespread and typical feature of 

 the Lockatong rocks, extending through many hundreds of feet of the 

 formation and throughout nearly all of the seventy miles of its exposed 

 length. It is also to be observed that the strongest rocks, massive argil- 

 Ktes whose unusual strength is dependent largely upon this cement, are 

 usually near the central part of the formation, both vertically and hori- 

 zontally, occupjdng the middle of the lens. 



The existence of the clay soil of the Lockatong belt is doubtless one- 

 very important reason why most of the early investigators of the argil- 

 lites described them as clay rocks, largely composed of kaolin or similar 

 substances. Our present studies, however, would rather lead us to be- 

 lieve that the kaolin, although really present in the soil, is derived, in 

 large part at least, from the alteration of feldspars which exist in the 

 rock in a fresh condition. 



Origix 



The general shape of the Lockatong as a whole, and its sediments of 

 such exceedingly fine grain and of such uniform texture, give evidence 

 of its mode of origin. Its present outcrop (Plate VII), and the com- 

 parison of detailed sections (Fig. 1, p. 149), indicate a lens-like shape, 

 with the finest sediments in the center of the lens, as might be true of a 

 series of sediments filling a basin. The densest and most massive rocks 

 of the series, the argillites, are remarkably uniform in character, being 

 of ver}^ even grain and without coarse layers through thicknesses which 

 may be great, as at Byram, where a single bed is forty feet thick, without 

 a well marked parting along any of the bedding planes. Through a thick- 

 ness of 3000 feet of beds in the Lockatong, there is scarcely a rock ex- 

 posed whose grains are large enough to be visible to the unaided eye. 

 Sedimentation during the time when these materials were deposited must 

 have been very regular, and the conditions very steady and uniform for a 

 long period. The presence of crustaceans and of ganoid fishes points- 

 clearly to the existence, at times, of considerable bodies of water or tern- 



