402 J. D. Dana on the Feldspar group of minerals. 
é Mica group has the following for the oxygen ratios 
between the bases and silica : 
Bases Silica Bases Silica 
1, Astrophyllite 1: 1 5. Muscovite : ly 
2. Phlogopite Sook 6. Lepidolite 1 : 1) 
3. Biotite 1 7. Cryophyllite 1 : 2 
as 
4. Lepidomelane 1 : 1 
Now the ratios of the non-alkaline to alkaline constituents of 
the protoxyd bases in these species, as deduced from the average 
results of analyses, are as follows : 
Non-alk. : Alk. Non-alk. : Alk. 
1. Astrophyllite 6 1-5. Muscovite it Se : 
2. Phlogopite So rs 6. Lepidolite 1: ae ik. 
8. Biotite ee 7. Cryophyllite almostsolely 4 
4. Lepidomelane 2-1: 1 
nas long described would probably have § “5 
‘Same fate. Gen first Saneeaced-s3 pied Rath last year 
