OCCLUSION OF IGNEOUS ROCK 407 



sandstone. This signified the projection of the outcrop above 

 the level of the Mesozoic Sea, its gradual disintegration and 

 probable extensive degradation. So far as the excavation of 

 the adjoining part of the Hudson River canyon has been pos- 

 sibly connected with erosion of a soft rock, it may be safer to 

 refer this to the visible outcrops of serpentinoid immediately on 

 both edges of the old bluff than to a hypothetical bed of dolomitic 

 limestone of whose occurrence no direct proof has yet been 

 found. ^ 



All the evidence points to a volume in the original stratum of 

 this soft and easily eroded rock far exceeding that of the present 

 ridge. The northern end of the mass at Hoboken consists of 

 light green serpentinoid, in part thinly foliated, with eastward 

 <^ip 75°> toward the river; strike S. 20° W. 



In general it presents the uniform fibrous texture usual in 

 rock serpentinoid, with admixture of brucite, marmolite, talc, 

 dolomite, calcite, aragonite, magnetite, chromite and other 

 minerals, mostly hydrated, in veins and seams. 



But the coarser mass on Staten Island, at the southern end 

 of this occlusion, whose thickness has been estimated at less 

 than 100 feet, consists largely of ophiolitic amphibolite and 

 gray, green or colorless amphibole schists, sometimes pyrox- 

 enic, besides actinolite, asbestus and tremolite rock, passing into 

 serpentine, steatite and talc-schist, chlorite-schist, limonite and 

 cellular quartz-rock. I have determined the specific gravity of 

 two specimens from the point north of Tompkinsville, viz.: 

 dark gray amphibolite, 2.863 5 ^ight gray tremolite-schist, 

 2.844. 



Descriptions of these serpentinoid outcrops have been already 

 published by J. D. Dana (1880-1881), N. L. Britton (1881), 

 L. P. Gratacap (1887). J. F. Kemp (1887), G. P. Merrill 

 (1889), F. J. H. Merrill (1896), and D. H. Newland (1901).- 



Some observations concerning the distribution of this sheet 

 deserve consideration. Its southern portion on Staten Island 

 overlies an outcrop of coarse pegmatite for a few rods along the 



iW. H. Hobbs, Bull. Geol. Soc. Am., XVI, 1905, 176-180. 

 ^Sch. of Mines Quar., XXII, 1901, 307-317, 399-410. 



