126 THE DAWN OP LIFE. 



variable quantities of magnesia, besides a notable amount of 

 potash. This alkali is, however, sometimes wanting, as ap- 

 pears from the analysis of a green- sand from Kent in England, 

 by that careful chemist, the late Dr. Edward Turner, and in 

 another examined by Berthier, from the calcaire grassier, near 

 Paris, which is essentially a serpentine in composition, being 

 a hydrous silicate of magnesia and protoxyd of iron. A com- 

 parison 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 grassier, near Paris. 

 Berthier (cited by Beudant, Mineralogie, ii., 178). 



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

 (cited by Eogers, Final Eeport, Geol. N. Jersey, page 206). 



III. Loganite from the Eozoon of Burgess. 



TV. Green-sand, Lower Silurian ; Eed Bird, Minnesota. 

 Y. Green-sand, Cretaceous, New Jersey. 

 YI. Green- sand. Lower Silurian, Orleans Island. 

 The last four analyses are by myself. 



I. n. III. IV. V. VI. 



SiHca 40-0 48-5 35-14 46-58 50-70 50-7 



Protoxyd of iron 24-7 22-0 8-60 20-61 22-50 8-6 



Magnesia 16-6 3-8 31-47 1-27 2-16 3-7 



Lime 3-3 2-49 1-11 



Alumma 1-7 17-0 10-15 11-45 8-03 19-8 



Potash traces 6-96 5-80 8-2 



Soda -98 -75 -5 



Water 12-6 7-0 14-64 9-66 8-95 8-5 



98-9 98-3 100-00 100-00 100-00 100-0 



