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belongs to the Hudson River slate series. This type of rock forms 

 the whole western side of the valley for several miles. Beds stand 

 on edge or dip steeply southeastward and are in good sound physi- 

 cal condition. The rock is everywhere a fine grained micaceous 

 slate or phyllite and in some places carries pyrite crystals. It is 

 impossible to estimate the thickness or minor structural habits. 

 But it is clear that it forms the upper member of a series that 

 has a synclinal structure and therefore the belt represented by 

 the phyllite marks the axis of the syncline although the chief val- 

 ley development lies wholly to one side. 



Limestone. Eleven borings (no. 2, 3D, 4 C, II, 13 C, 18, 

 22, 23, 25, 26 and 29) are in limestone. All show essentially a 

 very fine grained close textured crystalline gray or white or bluish 

 rock with strong bedding standing nearly vertical or at very high 

 angles. This, because of its character and relation to other forma- 

 tions, is regarded as the Wappinger limestone — a formation well 

 known north of the Highlands, where it is at least 1000 feet thick. 

 From present explorations it is now certain that a belt 3250 feet 

 wide is underlain continuously by this formation standing nearly 

 on edge. Unless repeated of course this would represent approxi- 

 mately the thickness for Peekskill valley. But it is not believed 

 to be so thick. It is moire likely that there is a threefold occur- 

 rence brought about by close isoclinal folding (a closed s-fold) 

 as seen in the accompanying cross section. This view is supported 

 by at least one occurrence of the underlying quartzite member near 

 the center of the valley at a point a couple of miles farther north 

 On the line of exploration, however, none of the borings pene- 

 trate any other formation beneath. Attention is called to additional 

 structural details and physical conditions in a later paragraph. 



Quartzite. One boring (no. 5) is in a quartzite. It is very 

 pure, fine grained, closely bound and typical quartzite. The beds 

 stand almost vertical and the whole thickness is known from nearby 

 outcrops to be approximately 600 feet. From its character and re- 

 lations to other formations it is regarded as the Poughquag — a 

 well known formation of the north side of the Highlands. 



Gneisses. Five borings (no. 7 E, 9 B, 17, 27 and 28) are in 

 gneisses. These are to a considerable extent simple granite gneisses 

 of igneous origin. But there is the usual variety characteristic of 

 the Highlands gneisses and no doubt they are representatives of 

 the great basal gneiss series that is elsewhere referred to as the 

 equivalent of the Fordham of New York city. 



