106 HISTORICAL GEOLOGY 



Nova Scotia. Lithologically this formation is quite variable, 

 being mostly shales and sandstones in the Appalachians and 

 central New York, and largely limestone in western New York and 

 farther west and southwest. This limestone does not imply deep 

 marine water, but merely shallow water comparatively free from 

 land-derived sediments. A remarkable and well-nigh universal 

 feature of the Clinton formation is its interstratined beds of iron 

 ore (hematite) . This iron ore is especially well developed through- 

 out the Appalachians, from central to western New York, 

 Wisconsin, and in Nova Scotia. The ore is concretionary or oolitic 

 in character and apparently a contemporaneous deposit enclosed 

 within the shales or limestones. It is often highly fossiliferous, 

 hence the name " fossil ore." 



Conformably above the Clinton beds lies the Niagara limestone, 

 which has a still wider distribution than the Clinton. Its type 

 locality is at Niagara Falls, and in New York state it is divided 

 into the Lockport and Guelph dolomitic limestone formations. 

 This mid-Silurian time was another great limestone-making age 

 almost comparable to that of the mid-Ordovician. In the United 

 States, Niagara limestone is known throughout much of the upper 

 Mississippi Valley and Great Lakes region, southward to Ten- 

 nessee, and westward to Missouri, Oklahoma, and northern Texas. 

 In Canada it is widely distributed in Manitoba, just west of 

 Hudson Bay, and in the Arctic Islands. Niagara limestone also 

 quite certainly occurs in parts of the western United States, 

 though definite correlations are not yet made. Coral reefs are of 

 common occurrence in the formation. It should not be understood, 

 however, that limestone was universally forming during Niagara 

 time, exceptions being, for example, Niagara shales in central 

 New York and in Nova Scotia. 



The Cayugan Series. — The Salina formation rests directly 

 upon, but is much less extensive than, the Niagara formation, 

 being found only through parts of Pennsylvania, New York, 

 Ontario, Ohio, and Michigan. Lithologically the formation is 

 quite variable, including all the common types of sediments as 

 well as waterlime (hydraulic limestone), red shales, and salt and 

 gypsum beds. The Shawangunk conglomerate, until quite recently 

 classed with the Oneida, is of Salina age. The eroded edges of its 

 resistant, tilted strata form the Shawangunk Ridge (so-called 

 Range) of southeastern New York and the Kittatinny Range of 



