252 ANNALS NEW YORK ACADEMY OF SCIENCES 



the amoimt of dynamic luetamorphisiii that it has undergone, it was evi- 

 dently intmded into the shales now represented by the mica schist prior 

 to the period of folding as an intrusive sheet. 



Pegmatite sheets and dikes become quite abundant in the mica schists 

 east of the Dover-Pawling Valley. These are usually present in the 

 form of intrusive sheets and lenses, parallel to the foliation of the schists 

 which in most cases also represents the bedding planes of this formation. 

 Dikes also occur. West of the Dover-Pawling Valley, the pegmatites are 

 not very prominent, occurring only occasionally in the schists just west 

 of this valley. The tourmaline noticed in one of the sections of phyllite 

 collected west of the Dover-Pawling Valley was probably derived from 

 emanations given off by these pegmatitic intrusions. 



HISTORICAL GEOLOGY 



As seen from the above description of the formations north of the 

 Highlands, a sandstone was laid down unconformably upon the upturned 

 edges of the folded pre-Cambrian gneisses during lower Cambrian time. 

 Then followed a period of limestone deposition which continued into 

 Trenton time. Sedimentation was not continuous during this entire 

 interval, but there were several retreats of the sea followed by re-ad- 

 vances, so that there are a number of breaks in the limestone represented 

 by disconformities. These can only be recognized on paleontological 

 evidence. The limestone deposition was followed by that of a thick 

 series of dark shales which range in age from Trenton to Cincinnatian. 



Then at the close of the Ordovician, there was inaugurated a period of 

 great orogenic movement, commonly known as the Green Mountain up- 

 lift. The formations described were thrown into a series of anticlines 

 and synclines whose axes have a northeast and southwest trend. Accom- 

 panying this folding, there occurred the intrusion of a large number of 

 pegmatitic sheets and lenses in the eastern portion of the area, which are 

 undoubtedly closely related to the granitic batholiths occurring still far- 

 ther East in Connecticut. The quartz diorite described from Haviland 

 Hollow, as already mentioned, was intruded prior to the folding. 



The burial of these formations to a depth sufficient to bring them into 

 the zone of anamorphism of Van Hise and the intense pressure accom- 

 panying the great orogenic movement which produced the folding to- 

 gether with the injection of a large amount of pegmatitic material had a 

 marked metamorphic effect upon the formation involved, causing the 

 limestone in the eastern portion of the area to become completely re- 

 crystallized and bringing about the formation of numerous lime and 

 other silicates in it while the overlying shale was converted into a mica 

 schist. 



