174 ANNALS NEW YORK ACADEMY OF SCIENCES 



in these states is more probably the result of normal processes of depo- 

 sition than of alteration by igneous or other later action. The cement is 

 for the most part silica, the origin of which is by no means easily estab- 

 lished, but which does not seem to require abnormal processes or later 

 altei-ation for its introduction. Some horizons in the Princeton area con- 

 tain regularly arranged strings of crystal cavities radiating downward in 

 conical groups. These seem to have been ciystals which grew in the sedi- 

 ments, while the latter were still soft. Their growth in wet muds per- 

 fectly agrees with the other known features of the rock, and they seem to 

 have a definite place in the sedimentary cycle of deposition. Their 

 unique arrangement is as yet unexplained. 



The Lockatong formation, while composed in the central part of mas- 

 sive argillites, is much more shaly on the margins, and passes by gradual 

 stages into the other Triassic formations above and below it, through a 

 series of dove-tailing strata. Hence its boundaries are very uncertain, 

 and large portions of its upper and lower parts may as well be said to 

 belong to the series above or below as to the Lockatong. Therefore it is 

 our conclusion, which is similar to that stated by Dr. H. B. Kummel,^® 

 that the Lockatong series, as a definite geological time unit, is probably 

 valueless, since part or all of the formations seem to be contemporaneous 

 with portions of the Stockton and Brunswick series elsewhere. 



There are three principal joint directions, the most important of which, 

 occupied by the major joint series (tension joints), is remarkably con- 

 stant in direction tliroughout the area. It affects all the Lockatong rocks, 

 and is also found on the borders of the intrusive diabase* mass of Rocky 

 Hill, an extension of the Palisade sill, but not far within the latter. 

 Titanium minerals — brookite and ilmenite — are found in these joints, 

 apparently far removed from diabase, together with analcite and barite, 

 whose derivation from the intrusive rocks is indicated by the occurrence 

 of the same minerals in similar joints in the immediate vicinity of the 

 trap rocks at Byram, Hunterdon Co., N. J., and elsewhere. The occur- 

 rence of such minerals in the joint cavities of sedimentary rocks, two 

 miles from the nearest visible igneous rock, is worthy of special note. 

 The hypothesis is advanced that these major joints were fonned very soon 

 after tlie intrusion of the igneous mass, at the beginning of a tectonic 

 disturbance which widely affected the Triassic beds ; and that later move- 

 ment took place along a very few major fault lines. 



'I'he Lockatong argillite is very dense and close grained, as shown by 

 experiment. This, together with its remarkable siliceous cement and the 



2sKu.mmi:l. II. p.. Kept. State Geologist of N. J. for 1897, p. 41. 



