372 GEOLOGY. 



were deposited on land, or in an enclosed body of water not freely- 

 connected with the sea. On the other hand ; the materials of some 

 parts of the formation are so perfectly assorted, and the pebbles 

 so thoroughly rounded, as to suggest wave rather than stream work. 

 If the formation is of marine origin, the coarseness of the sediments 

 may help to explain the absence of fossils, for where coarse sediments 

 are gathering, shells are more likely to be destroyed, and so far as 

 they are buried, they are likely to be dissolved at a later time because 

 of the free circulation of water through the porous beds. 



South of Lake Ontario there are beds which have been classed as 

 Oneida. They are fossiliferous and clearly associated with the Medina 

 formation of the region. They are believed to have been deposited 

 in waters which were separated from the Appalachian basin already 

 referred to. The term Shawangunk, applied to the eastern beds, is 

 not applied to the more westerly ones. 



The Shawangunk (or eastern Oneida) formation is about 500 feet 

 (maximum) thick in New York, and 800 feet in Pennsylvania. Both 

 in its constitution and structure it bears the marks of shallow water 

 (or subaerial) deposit, being chiefly of sandstone and conglomerate, 

 often cross-bedded and ripple-marked. The materials of the forma- 

 tion seem to have been derived from older lands to the east. They 

 are essentially quartzose, and represent the products of rock decay 

 rather than of rock breaking. The abundance of quartz pebbles sug- 

 gests that the metamorphic rocks of Appalachia had long been under- 

 going decay before the advent of the Oneida epoch, but that the land 

 surface had stood so low as not to allow of the removal of the coarser 

 products of decomposition. If, following such a period, the land 

 were elevated, rejuvenating the streams, such material as that of 

 which the Oneida formation is composed would have been washed 

 down to the sea or to low-lying lands. The character of the Ordo- 

 vician beds (limestone and fine sediments) in the region of the Oneida 

 formation is consistent with the sequence of events here suggested. 



The Oneida formation, composed at the outset of durable materials, 

 has been so thoroughly indurated by compression and cementation as 

 to become exceedingly obdurate. The outcropping edges of its tilted 

 beds (Fig. 171) constitute the crest of the Kittatinny range in New 

 York, New Jersey, and Pennsylvania (Fig. 172). Not only does the 

 Oneida conglomerate constitute the crest of this range, but the range 



