300 APPENDIX 



glauconites differ widely in composition. The 

 variety best known, and commonly regarded as the 

 type of the glauconites, is that found in the green- 

 sand of Cretaceous age in New Jersey, and in the 

 Tertiary of Alabama ; the glauconite from the 

 Lower Silurian rocks of the Upper Mississippi is 

 identical with it in composition. Analysis shows 

 these glauconites to be essentially hydrous silicates 

 of protoxyd of iron, with more or less alumina, and 

 small but variable quantities of magnesia, besides a 

 notable amount of potash. This alkali is, however, 

 sometimes wanting, as appears from the analysis of 

 a green-sand from Kent, in England, by that care- 

 ful chemist, the late Dr. Edward Turner, and in 

 another examined by Berthier, from the calcaire 

 grossier, near Paris, which is essentially a serpentine 

 in composition, being a hydrous silicate of magnesia 

 and protoxyd of iron. A comparison of these last 

 two will show that the loganite, which fills the 

 ancient Foraminifer of Burgess, is a silicate nearly 

 related in composition. 



I. Green-sand from the calcaire grossier^ near 

 Paris. Berthier (cited by Beudant, " Mineralogie," 

 ii., 178). 



II. Green-sand from Kent, England. Dr. Edward 



