MUSEUM OF COMPARATIVE ZOOLOGY. 270 



it seems hopeless to look for them here, and I was unable to get good 

 evidence as to the position of the trap. It is surely intrusive, as no 

 amygdaloid is present, and the shales are baked on both sides of the 

 trap ridges ; but whether interbedded or in dike form, is rather an 

 open question. Against the sheet form may be noted the small dif- 

 ference in slope of the two sides of Sourland Mountain, and conse- 

 quently the abseijce of a well-marked face and back so characteristic 

 of the sheets elsewhere ; and the fact that the baked and blackened 

 shale ascends to about the same height on either slope (Cook, b, 191). 

 Farther southeast, the several elevations known as Rocky Hill, Penning- 

 ton Mountain, and Bald Pate are on the other hand probably sheets, 

 as their southern fi\ce is steeper than the northern : as suggested by 

 Russell, these are presumably the reappearance of the Palisade curve, 

 which is covered by the cretaceous strata in its middle ; its length from 

 Haverstraw on the Hudson to Bald Pate on the Delaware would then 

 be over eighty miles. 



4. BRIEF STATEMENT OF FORMER VIEWS. 



The following paragraphs show in brief the opinions of various writers 

 on this subject, the districts of their observations, and the dates of their 

 publications. 



It was thought that the trap was intrusive by Silliman (Conn., 1810, 

 1830), Hitchcock (Mass., Conn., 1818), Chapin (Conn., 1835), Gesner 

 (Nova Scotia, 1846), Lyell (Va., 1847), Emmons (N. Y., 1846, N. C, 

 1858), Cook (N. J., 1868), E. S. Dana and Hawes (Conn., 1874), KeiT 

 (N. C, 1875), Prime (Pa., 1875), and Frazer (Pa., 1876). These authors 

 make no special reference to the effect of the eruptions on the position 

 of the sandstone strata in their writings of the above dates. It was 

 held that the intrusion of the trap tilted the sandstones by A. Smith 

 (Conn., 1832), Percival (Conn., 1842), Emmons (1854), and in part by 

 Silliman Jr. (Conn., 1842) and Hitchcock (Mass., 1844). 



The following considered the trap intrusive, but held that the dip of 

 the sandstone was due to some other disturbing force : Jackson and 

 Alger (Nova Scotia, 1833), H. D. Rogers, (N. J., 1836), Hitchcock in 

 part (Mass., 1844), Credner (N. J., 1865), J. D. Dana (Conn., 1863- 

 1880), Heinrich (Va., 1878), and Russell (N. J., 1875-1880). 



The overflow origin of the trap was faintly suggested by Gibson (Pa., 

 1820) and Cooper (N. J., 1822) ; it was shown to be probable by 

 Hitchcock in 1833, and proved later (Mass., 1841-1858); Dawson came 



