164 The Petrography and Genesis of Sediments 



(2) The diagram offers little of special interest. It is moderately well 

 sorted sand, intermediate between lagoon and marine conditions, but 

 nearer those of a lagoon. The usual absence in the Monmouth of the black 

 clay peculiar to the Matawan combined with this fairly good sorting sug- 

 gests more open water conditions, that is, probably a more general sub- 

 mergence. The most striking feature of the sediment is its great coarse- ' 

 ness which, with its regular bedding and uniform lateral extension in the 

 field, points to near-shore conditions for its formation. This leads to the 

 third important feature to be noted, namely, 



(3) The fact that in such shallow near-shore conditions glauconite is 

 present. This is so contrary to the usual assumption of quiet waters for 

 the formation of glauconite that one is inclined to believe that the glau- 

 conite is reworked from adjacent shore bluffs, but in that case evidence 

 of wearing of the glauconite grains would be expected. Still the author 

 does not believe that any modern glauconite-bearing sediment as coarse 

 and as free from clay as this has been found. 



Another possibility which suggests itself is that the sediment was 

 formed in deeper water but swept by a strong current. While there are 

 no data for the transporting power of currents in open water it is doubt- 

 ful that so much of the " coarse " sand could be transported by such 

 means. Moreover, the regularity of bedding in the field is against that 

 assumption. 



It is a peculiar sediment and all the more interesting, not only for its 

 peculiarities, but also because in its general appearance in the field it is 

 so typical of the Monmouth formation of the Chesapeake Bay region. 



(4) Finally, an important feature is the high percentage of feldspars 

 and their appearance of freshness. Their freshness opposes the belief 

 that the material is reworked from an older sediment, while their high 

 proportion, as well as the grain of combined quartz and feldspar noted in 

 the description of the coarse sand, point to origin from nearby. 1 



1 For the percentage of feldspar in different deposits see Mackie, Win. 

 The sands and sandstones of E. Moray, Trans. Geol. Soc. Edinburgh, 1896, vol. 

 7, p. 149. 



