W. E. Darton — -Trap of New Jersey. 137 



eruptive materials apparently scoria and tuff, and at other lo- 

 calities the sheet is seen to be composed of successive flows, the 

 base of one lying on the vesicular surface of a preceding flow, 

 in one case with an intervening layer of trap breccia at some 

 points. 



In thickness the first Watchung trap varies from 450 to 650 

 feet, the second, from 600 to 850 feet, and the third, from 225 

 to 350 feet in the main, and the area enclosed by the outermost 

 hooks is about 500 square miles, no doubt in greater part under- 

 lain by trap, so that the Watchung sheets represent lava-flows 

 of no mean volume. Apparently the extrusions were continu- 

 ous throughout, for excepting the intercalated breccia above 

 alluded to, no intervening or overlapping sedimentary materials 

 were discovered. The absence of fragmental volcanic deposits, 

 excepting the local beds at the base of the second Watchung 

 sheet, is a noteworthy feature, and the first extrusions were not 

 attended by ejections of scoria, ash, etc., or, at most, in suffi- 

 cient amount to extend to the present lines of outcrop. The 

 eruptions which gave rise to the Watchung trap masses were 

 no doubt very similar to those of some of the great lava-flows 

 of the western part of the United States, which appear to have 

 welled forth from long fissures without attendant craters, or 

 the ejection of fragmental materials. 



The great hooks characterizing the southernmost outcrops of 

 the Watchung traps are entirely due to flexure, and the bowed 

 course of their northern terminations and of Towakhow Moun- 

 tain are due to the same cause. 



The New Yernon trap, across the Great Marsh from the 

 Watchung Mountains, is apparently an extension of one of the 

 Watchung flows brought up by the partial quaquaversal which 

 determines its crescentic course, and it is similar to them in 

 every respect but not so well exposed for study, while the New 

 Germantown traps farther south westward, but at approximately 

 the same horizon, are undoubtedly extrusive and may be 

 remnants of another extension of the Watchung flows. 



The Palisade trap is the best exposed instance of intrusion 

 on a large scale in New Jersey and although it is in greater 

 part an essentially conformable sheet throughout, the supply 

 dike from which the sheet extends reaches the surface north- 

 west of Hoboken and in Rockland County, New York, along 

 the inner side of the ridge and is in part finely exposed in the 

 two tunnels of the West Shore railroad. 



For many miles along the Hudson River the Palisade sheet 

 is exposed in contact with the underlying strata near the base 

 of the formation, and while the relations are essentially con- 

 formable throughout, local irregularities are frequent in which 

 the ragged edges of the strata are crossed laterally up or down 



