300 ANNALS NEW YORK ACADEMY OF SCIENCES 



Island^* in 1887 described the formations underlying the island, with a 

 discussion of their mineralogical composition, origin and structural rela- 

 tionships. 



During the late 80's, Dr. F. J. H. Merrill did much field work for the 

 New York State Survey and the United States Geological Survey in the 

 southeastern part of the State both in the Highlands themselves and in 

 the metamorphic area to the south. In his first paper^^ in 1890 on these 

 formations, he describes, under the term "Manhattan Group," the Man- 

 hattan schist, Inwood limestone, and Fordham gneiss, and states that he 

 is in doubt as to whether to place this group in the pre-Cambrian or to 

 correlate it with the slates, limestones and quartzites of Ordovician and 

 Cambrian age north of the Highlands. The fact that there is a marked 

 unconformity between the lower Cambrian quartzite and the pre-Cam- 

 brian gneiss north of the Highlands and that no such unconformity has 

 yet been found between the Manhattan Group and the underlying beds 

 south of the Highlands would seem strong evidence against such a corre- 

 lation. On the other hand, he points out that no unconformity has yet 

 been found between the partly metamorphosed strata of Peekskill Hollow, 

 Tompkins Cove and Verplanck's Point, which he considers to be of Ordo- 

 vician age, and the metamorphic beds of the Manhattan group which 

 ^adjoin them, although such an unconformity would be expected if the 

 latter are of pre-Cambrian age. In a later report^® he makes the state- 

 ment that the two series are equivalent, basing his conclusion on the rela- 

 tion of the quartzite, limestone and schist of Westchester County to the 

 underlying gneiss, as this relation is precisely similar to that of the Paleo- 

 zoic strata in southern Dutchess County and Putnam County to the sub- 

 jacent gneiss, and from the nearly complete stratigraphic continuity. 

 This statement apparently is contradictory to the one made in the previ- 

 ous paper quoted, where attention was called to the fact that there was a 

 marked unconformity north of the Highlands, while none such had been 

 found to the south. The Fordham gneiss of the Manhattan group, as 

 previously defined, is considered to be pre-Cambrian in age, possibly Al- 

 gonkian. The break between it and the Paleozoic is thought to be marked 

 by a stratum of thinly bedded quartzite which crops out occasionally and 

 is followed by the Inwood Limestone. 



14 "The geology of Manhattan Island." Trans. N. Y. Acad. Sci., Vol. VII, pp. 49-64. 

 1887. 



^ "On the metamorphic strata of southeastern New York." Am. .Tour. Scl., 3rd ser., 

 Vol. XXXIX, pp. 383-392. 1890. 



" F. J. H. Merrill : "The geology of the crystalline rocks of southeastern New York." 

 50th ann. rept. N. Y. State Mus., Vol. I, pp. 21-31. 1896. 



