GEOLOGY OF THE PORT LEYDEN QUADRANGLE 21 



ite) ; 40^ of green hornblende and green augite and 5^ of hyper- 

 sthene, magnetite, biotite, zircon and apatite. This type is in 

 contact with another gabbroic rock which has a considerable 

 percentage of quartz and hypersthene and some microperthite. 



7 Very dark, long, narrow patches which are probably inclu- 

 sions are common. They usually consist mostly of decomposed 

 hornblende and basic plagioclase together with some quartz, 

 magnetite and biotite. 



Undetermined Precambric areas 



Unfortunately several large Precambric areas are so deeply 

 buried under Pleistocene deposits that the character of the un- 

 derlying rocks is entirely unknown. These areas have been so 

 indicated upon the geologic map. 



PALEOZOIC ROCKS 

 The Paleozoic rocks occupy a little over one half the area of 

 the quadrangle on the west side. Except at the extreme south 

 they always lie to the west of Black river. The maximum thick- 

 ness of the Paleozoic formations is approximately 1500 feet. 



Potsdam sandstone 



The Potsdam sandstone is of upper Cambric age and is the 

 most ancient sedimentary formation bordering the Adirondacks. 

 It is not present in outcrop in the Port Leyden quadrangle nor 

 in fact along the whole southwestern border of the Adirondacks, 

 although it is most likely present beneath the later formations. 

 South of Port Leyden the deep wells at Utica and at Rome show 

 a basal sandstone which is more than likely the Potsdam. West 

 of Port Leyden the Potsdam, according to Orton,^ is most cer- 

 tainly present in the deep wells of Oswego county at Central 

 Square, Parish, Pulaski and Stillwater. The nearest outcrops 

 of the sandstone are something like 20 miles north-northwest 

 of the Port Leyden quadrangle and from there northward to the 

 St Lawrence it is a common surface rock. 



Pamelia limestone 



The Pamelia limestone was named by Professor Cushing from 

 a town in Jefferson county where he recently recognized it as 

 a distinct formation.^ Between the Potsdam and the Pamelia, 



' Petroleum and Natural Gas in New York. N. Y. State Mus. Bui. 30. 

 1899. 



Geol Soc. Am. Bui. 1908. 19:155-76. 



