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CHAPTER I. 



OF THE UPPER SECONDARY SERIES, EMBRACING THE GREENSAND 

 FORMATION. 



General Description. — Adopting as hitherto the ascending order, 

 we shall describe first the upper secondary formations lying to 

 the northwest of the line above designated. This series includes 

 naturally five separate sets of beds, the characteristic features 

 and composition of which, commencing with the lowest, are as 

 follows : 



Fii'st. A group of sands and clays of several colours and 

 of somewhat variable constitution, but frequently of extreme 

 whiteness and remarkable purity. Among these occur beds of 

 pure potters' clay. This division of the general series rests, along 

 its northwest margin, from the Raritan to the Assunpink, in an 

 unconformable manner upon the middle secondary rocks, and 

 from the Shipetaukin to the Delaware upon the upturned strata 

 of the primary belt. It contains towards its upper beds much of 

 the dark blue sandy clay, which is also associated with the over- 

 lying greensand, from which it is not separated by any well- 

 defined limit. 



Second. A somewhat mixed group, consisting of beds almost 

 wholly composed of greensand in a loose and granular condition, 

 alternating with and occasionally replaced by layers of a blue, 

 sandy, micaceous clay. This is the " greensand formation," 

 properly so called. The greensand having become extensively 

 employed in agriculture as a ferliliTier of the soil, the bed in 

 which this mineral is the chief ingredient has acquired the name 

 of marl. The various features assumed by these strata in the 

 different parts of the extensive tract which they occupy, will be 

 specified in another place. 



Third. Immediately overlying the greensand formation near 

 its southeastern border, we find several limited exposures of a 

 yellowish granular limestone of rather crystalline structure, 

 and frequently siliceous composition. This rock exists in rather 



