244 ANNALS NEW YORK ACADEMY OF SCIENCES 



the accompanying heated waters in little crevices which had been de- 

 veloped after the period of folding had come to an end. In the modem 

 view,^^ zeolites are believed to have been deposited by heated waters ac- 

 companying the last stages of igneous activity. The mere leaching of 

 the necessary constituents by surface waters in the belt of weathering is 

 not considered sufficient. Professor Brogger^^ has also described zeolites 

 from pegmatite dikes where they occur as products of the last stages of 

 crystallization. 



Summary 



The Manhattan schist is a series of much metamorphosed argillaceous 

 and sandy shales, argillaceous sandstones and arkoses which represent a 

 thickness of several thousand feet. The argillaceous sediments were laid 

 down conformably upon the underlying limestone, the limestone grading 

 into calcareous shales at the contact. After their deposition, they were 

 penetrated by a series of basic igneous rocks, largely in the form of sheets 

 and sills. Then a period of great orogenic movements set in which 

 brought about intense folding in the whole area. The original sediments 

 had been buried to a sufficient depth to come into the comparatively 

 shallow zone of anamorphism for shales. A large series of granitic in- 

 trusions accompanied the folding. The granites are huge batholiths 

 which have only been exposed by later erosion at the surface in a few 

 places in this area. Radiating from the batholiths are numerous granitic 

 and pegmatitic dikes. During the earlier stages, the intrusions occurred 

 mainly along the bedding planes which were the lines of weakness, and 

 in many places the rock was so thoroughly injected in this manner that 

 it has become an injected gneiss. 



The burial to a considerable depth and the intense stress set up by the 

 orogenic movements which produced the folding, together with the meta- 

 morphic effects of the granitic and pegmatitic intrusions, brought about 

 the recrystallization of the constituents of the original shale and asso- 

 ciated sediments into mica and related schists. The earlier basic in- 

 trusives were also involved in the dynamic metamorphism. The metamor- 

 phism appears to be least pronounced north of Croton Village and in 

 those places in the vicinity of Peekskill where the schist did not come 

 under the influence of the local contact metamorphic effects of the Cort- 

 landt series. 



''O Waldemar Lindgren : "Some modes of deposition of copper ores in basic rocks." 

 Econ. Geol., Vol. VI, pp 687-694. 1911. 



"Zeits. f. Kryst. u. Miner.. 16 Band, pp. 168-173. 1890. 



