DISTRIBUTION UNITED STATES 627 



another.. Each one is covered with a sheath of basic glass (tachylite), 

 varying from a thin film to an inch or more in thickness, and thin sec- 

 tions show that this passes gradually into the holocrystalline mass of the 

 interior. The glass is very brittle and has a tendency to shell off parallel 

 to the surface on exposure to the weather or when struck with a hammer. 

 Hence it is very difficult to collect a specimen of the crystalline rock with 

 the glass still attached to it. 



In the First Mountain pillows, in striking contrast with those of Second 

 Mountain, there are few amygdules, and these are small and chiefly near 

 the surface coating of glass. On the other hand, many of the masses have 

 a central "pipe" or cavity from 1 to 6 or 8 inches in diameter, many of 

 these being flattened parallel to the bedding of the sedimentaries (plate 

 17, figure 1). Eadial columnar jointing is a common characteristic of 

 the spheroids and is especially well shown in weathered sections, as in the 

 upper portions of quarry walls. The spaces between the masses are partly 

 filled (in some places entirely so) with angular fragments of glass like 

 that which coats the individual pillows. This has generally been cemented 

 into a breccia by the deposition of quartz, calcite, a great variety of zeo- 

 lites, and many other less common minerals. 



At Great Notch (plate 17, figure 1) a structure in every way similar 

 to that at West Paterson forms the south wall of the trap quarry near the 

 railroad station, where a thickness of 40 to 50 feet has been exposed. 



At Glenside Park (Feltville) the pillow structure outcrops one-fourth 

 of a mile east of the bridge in the narrow ravine of a brook that drains 

 the northwestern slope of First Mountain. Spheroids and irregular pil- 

 lows are exposed in the bottom of the ravine and in several old prospect- 

 ing pits, locally known as "the copper mine," while the banks of the brook 

 show a similar structure and its relations to the overlying shale (figure 

 2). The interstitial material is a mixture of shale and angular fragments 

 of glass. The lava here is somewhat vesicular, many of the masses having 

 elongated tubular vesicles, 3 to 4 inches long and one-fourth of an inch 

 or less in diameter, set at right angles to their outer surfaces. Most of 

 these tubes are filled with chlorite, calcite, quartz, and zeolites. EusselP^ 

 reported the finding of some that contained a brilliant jet-black bitumen. 



At Glenside Park (Feltville) the pillow lava occurs immediately at the 

 upper surface of the flow (see figure 2) and extends downward to an 

 undetermined depth. A maximum depth of 10 or 12 feet is visible in the 

 banks and the old prospecting pits, and the structure is typically devel- 

 oped in the bed of the brook. The overlying shales rest on the uneroded 



®^ I. C. Russell : The occurrence of a solid hydrocarbon in the eruptive rocks of New 

 Jersey. Am. Jour. Sci. (3), vol. xvi, 1878; pp. 112-114. 



