28 NEW YORK STATE MUSEUM 



are mixed. Even this method has disadvantages because of the 

 difficulty of determining how much is due to mixture and how much 

 is due to original individual variation, but it will lead to much less 

 error and confusion of interpretation than to draw sharp lines of 

 separation. This method, therefore, has been adopted as suitable to 

 the purpose of this particular study and it is to be understood that 

 where the colors are single or simple, it is the authors' judgment 

 that the rocks are fairly distinct and distinguishable, but that where 

 the colors overlap, the rocks are intermediate and probably mixed. 



Individual formations mapped. On the basis explained above, 

 the following formations have been determined as mappable. 

 A Oldest metamorphics 



1 The Grenville series of metamorphis sediments (the oldest 



formation). 

 B The older great igneous members 



2 An old injection or impregnation type of Diorite gneiss of 



uncertain relation to the other types except that it is inti- 

 mately associated with the Grenville and is judged to 

 be the oldest intrusive. This may be referred to as the 

 Peekskill diorite gneiss or the PocJiuck gneiss. 



3 The Canada Hill granite and gneissoid granite with a multi- 



tude of variations. 



4 The Rescii'oir granite and gneissoid granite, a xenolithic 



granite with many variations. 



5 The Storm King granite and gneissoid granite with its 



injection borders. 

 C Crystallines of doubtful relation and age 



6 Lowerre qiiartsite, not occurring in this district in large 



enough development to map. (Apparently conformable 

 with the Grenville structure) 



7 Imvood limestone. A crystalline limestone. The same rock 



that forms the limestone valleys of southeast New York, 

 south of the Highlands to New York City. 



8 Manhattan schist. A mica-schist, undoubtedly to be cor- 



related with the extensive development of mica-schist 

 overlying the Inwood limestone of the district south of 

 the Highlands. 

 D The Cambro-Ordovician series 



Pnuqhqnag quartsite. (Clearly unconformable on the 



Highland gneisses) 

 lo Wappinger limestone. (Conformable to the Poughquag) 



