20 ANNALS NEW YORK ACADEMY OF SCIENCES 



brian."' The writer is not aware of any elastics in the Cortlandt Series. 

 nor does there seem to be any justification for calling the series Lower 

 Cambrian. There is a general lithologic similarity with the upper series 

 of the Adirondack's, but the almost entire absence of metamorphism in the 

 Cortlandt Series, coupled with the surprising freshness of the olivine 

 present, are rather strong indications of a considerably later date. The 

 Triassic trap of New Jersey is so entirely different in structure that the 

 Cortlandt Series has probably no relationship with it ; and from the litho- 

 logic character of later igneous masses and from the fact that no meta- 

 morphism has taken place in the East since the Permian, it is practically 

 certain that the series is not post-Permian. Kemp's study of the Rose- 

 town extension fully confirms this view ; he finds 21 that the rocks here cut 

 the (Cambrian) Tompkin's Cove limestone but have not disturbed the 

 Triassic sandstones. Hobbs's work in Connecticut is also entirely con- 

 cordant. The whole expanse of the Paleozoic is, however, open; and 

 while nothing can be definitely said, it is the writers opinion that the 

 Cortlandt Series is younger than is generally supposed, more probably 

 late Paleozoic than early Cambrian. 



Petrology 



In the following descriptions of the various types, the rocks will be con- 

 sidered in the order of their acidity, and frequent reference will be made 

 to the large geological map. In the case of the common rock minerals, at 

 least, an effort has been made to condense as far as possible the mass of 

 data which has accumulated from the description of the 260 slides exam- 

 ined and to render the optical descriptions reasonably brief and succinct. 

 In every case, the fullest description of the various minerals is given 

 under the important rocks in which they are the most abundant or of 

 which they are the most typical. Williams, in the papers cited above, has 

 sometimes given fuller and more minute optical discussions of the min- 

 erals than is here considered necessary. 



PLUTONIC ROCKS 



Granite 



The granite member of the series lies to the northeast of the main bodv 

 and extends from south of the Crompond Eoad northward to Lake Mohe- 

 gan. It covers an area of about 3f miles, and throughout its extent it 

 appears to be very uniform in texture and composition. The exact bor- 



21 Op. cit., p. 25.°,. 



