THE GREENSANDS OF NEW JERSEY. 1 69 



than 900 fathoms, and most commonly takes place between 100 

 and 200 fathoms. The entrance of large rivers into the sea or 

 the prevalence of strong currents would tend to interfere with 

 its formation, so that the area of distribution of greensand is 

 seldom continuous for great distances. 



Although greensand is not known to be formed except in 

 the presence of land-derived materials its production is accom- 

 plished through the intervention of foraminifera. Their connec- 

 tion with the formation of glauconite was first shown by Ehren- 

 berg^ in 1855 as the result of a study of greensand from many 

 deposits in Europe and America. Professor Bailey^ the succeed- 

 ing year stated that the formation of greensand is likewise taking 

 place on the floor of existing seas, and under the same conditions 

 that existed in past geological ages. 



According to Murray and Renard the chambers become 

 filled with muddy sediment, and "if we admit that the organic 

 matter enclosed in the shell, and in the mud itself, trans- 

 forms the iron in the mud into sulphide, which may be oxidized 

 into hydrate, sulphur being at the same time liberated, this sul- 

 phur would become oxidized into sulphuric acid, which would 

 decompose the fine clay, setting free colloid silica, alumina being 

 removed in solution ; thus we have colloid silica and hydrated 

 oxide of iron in a state most suitable for their combination." 

 The potash which is necessary to complete the composition of 

 glauconite may be derived from the decomposition of the frag- 

 ments of crystalline rocks or their common constituents, ortho- 

 clase and white mica. 



Two conditions then are requisite for the production of glau- 

 conite, first the deposition of mineral particles of land-derived 

 origin ; and second, the presence of foraminifera. In the 

 absence of either the production of greensand will not take place. 

 It is further seen that the formation of greensand is retarded 

 and finally ceases altogether as the amount of deposition of 

 land-derived materials increases adjacent to the coasts. Only 



' Abhandl. d. k. Akad. d. Wissenschaften zu Berlin, 1855, pp. 85-176. 

 =* Boston Soc. Nat. Hist., Proc, Vol. 5, 1856, pp. 364-368. 



