256 ANNALS NEW YORK ACADEMY OF SCIENCES 



of this formation with the Hudson River series He bases his conclusions 

 upon a number of facts. 



One is the relation of the Peekskill Valley quartzite, limestone and 

 phyllite to the crystalline limestone in the Sprout Brook valley. Dr. 

 Berkey considers the former to represent a down-faulted block of the 

 Poughquag-Wappinger-Hudson River strata, as already mentioned, while 

 the latter, he thinks, is the equivalent of the Inwood, on account of its 

 thickness and lithological resemblance to that limestnoe, and that it is 

 not one of the interbedded limestones occurring in the pre-Cambrian 

 Highland gneisses farther north. In the Peekskill Valley, there are five 

 hundred feet of quartzite corresponding to the Poughquag quartzite, 

 while in the Sprout Brook valley the limestone apparently rests upon the 

 gneiss. This limestone, moreover, is very much more metamorphosed 

 than that occurring in the Peekskill Valley. All these facts go to show 

 that they cannot be correlated, and that if the former is the Inwood, the 

 latter must be later in age. 



Another strong argument against such a correlation is that a quartzite 

 rarely appears between the Inwood limestone and the underlying Ford- 

 ham gneiss, and where it does occur it is quite thin and can be followed 

 for only a short distance. Where it is present, it appears to be a part of 

 the gneiss, as it is conformable with it and apparently grades into it. At 

 other places, the Inwood limestone rests conformably upon the Fordham 

 gneiss. North of the Highlands, on the other hand, the Poughquag 

 quartzite is usually well developed and reaches a thickness of six hundred 

 feet in places. It rests unconformably upon the pre-Cambrian gneisses 

 which Dr. Berkey^^ believes are the equivalent of the Fordham gneiss. If 

 the two series of formations are equivalent, it is hard to understand why 

 there should be such a marked unconformity north of tlie Highlands, 

 while to the south they are apparently conformable. Evidently such a 

 correlation is impossible the Highland gneisses are of the same age as 

 the Fordham gneiss of southeastern New York. In this connection, how- 

 ever, it is interesting to note that in most of the places where the contact 

 between the pre-Cambrian gneisses and Cambrian quartzites, schists and 

 conglomerates is exposed in northwestern Massachusetts and western Ver- 

 mont, the two formations are in apparent conformity.^*^ There are other 

 localities in this same region where they are unconformable. The work 

 of Pumpelly, Wolff and Dale in the Green Mountains of Massachusetts 

 showed that this conformity was only an apparent one and that the for- 



«* Op. cit., p. 361. 



•"T. Nelson Dale: Structural details In the Green Mountain region and in eastern 

 New York. U. S. Geol. Surv. RuU. lOH, p. 18. 1002. 



