294 BULLETIN OF THE 



absence of amj'gdaloid here (mentioned once on 403), and the frequent 

 mention of indurated sandstones above as well as below the trap. The 

 sandstone near the trap by East Rock (W. S. I. 1) * "is remarkably in- 

 durated to an unusual width " (395). Two points on the back of East 

 Rock show "highly indurated sandstone" bordering the trap (396). 

 Mill Rock (W. S. I. 2) is a dike rather than a sheet, and is bordered by 

 "light gray very indurated coarse sandstone" (396). West Rock 

 (W. S. I. 4) is overlaid or bordered on the east by indurated sandstone 

 (399). The dikes or ridges of W. S. I. 7 are bordered b}"- "singularly 

 altered and indurated" sandstone (401). Roaring Brook shows indu- 

 rated sandstone on the back of W. S. II. (403). "At different points, 

 in connection with the western line of trap," dark purple, black, and 

 bright indurated sandstones are found (437). Professor Dana classes 

 East and West Rock, Mount Carmel, and the Meriden Hills with the 

 dikes of Pine and Mill Rock, as trap "that came up melted through 

 wide fissures in the sandstones and subjacent rocks " (cZ, 46). 



The Palisades give the largest example of intrusion : this origin was 

 first well proven for them by Russell (d ; see also our observations, H, J) ; 

 Emmons noted, a number of yeai's ago, that branching intrusions oc- 

 curred in the sandstones below (6, 200; his figure is here copied, 16). 

 Smaller sheets are found in New Jersey at Martin's Dock (N), and on 

 the Delaware (0) ; whether the large coarse trap masses by Lambert- 

 villa (P) are dikes or sheets, I cannot fully decide ; but they are not 

 overflows. Cook inclines to the intrusive origin of all of these {b, 176, 

 200) ; he mentions the occun-ence of transverse dikes by Hook Moun- 

 tain, the north end of the Palisade Range (c, 32), which would seem to 

 correspond to the large dikes by West Rock, Conn. H. D. Rogers's 

 sections represent intruded sheets in the Pennsylvania sandstones near 

 the surface (here copied, fig. 23) ; and Frazer says of the traps about 

 Lancaster County, "As a general rule in this region, their dip corre- 

 sponds to that of the beds between which they were poured out " (6, 318; 

 compare with the quotation above, under Dikes). 



W. B. Rogers describes the trap in Virginia as "not unfrequently 

 entering between the layers of sedimentary rock, or pouring out and 

 overspreading them at the top" (6, 82) ; and Lyell writes of the trap 

 in the Richmond coal field that it, "although intrusive, has often here, 

 as is so common elsewhere, made its way between the strata like a con- 

 formable deposit." But all these latter references are inconclusive as to 

 intrusions or overflows ; they leave the question open for further work. 



* The notation used by Percival. 



