1889.] Mineralogy and l\'trography. 813 
silicates, by regarding meta-silicic acid as as a union of ortho- and 
poly-silicic acids (H.SiO, + H^Si/), = 4H^Si03), and di-silicic acid 
as a poly-silicic acid from which ortho-silicic acid has been separated 
(3H, Si30« — H, SiO,= 4H, Si,0,)- ^i^he advantages of this view, as 
suggested by the author, are found in tlie discussion of the decomposi- 
tion of natural silicates, and in the study of isomorphism in long series 
of isomorphous substances like the feldspars, and in the di-morphism 
meta-sihcates, their dimorphism may be explained by supposing the 
base in the one case to replace the hydrogen in the ortho-acid, while 
in the other it may be supposed to be united with the residue of the 
poly-acid. According to this view all silicates may be regarded as 
salts of ortho- or of poly-silicic acids or their combinations. The 
iron .sulijhates of Chili are at present the subject of careful work by 
chemists in this country and abroad. The investigations of Frenzel *^ 
and G. I,inck '"' have already been noticed. Recently Mackintosh^ 
amarantiir, and a W\\ other sul)staiux-s with apparently definite com- 
positions. A |)iilvcrultiu llaky orange-colored substance associated 
with copiapite and amarantitc lias a composition corresponding to 
(FeO)Fe.(S(\X-f 4H./). ^^hite pulverulent decomposition pro- 
ducts of the above mentioned minerals are basic iron sulphates and 
combinations of ferrous sulphate with the corresponding sodium com- 
pound. Among the minerals described by the author is one to which 
groups of a pale green color, forming nearly spherical nodules, like 
wavellite. It is soluble in water, and has the composition : 
SO, Ke.,(A, Al,(), Xa,C) I^O SiO, H.p 
itonriif- 
ulin. 
Mace 
\2 
. Na,F 
e(So 
.).+ 3H 
^0. In the Archaean lime- 
s' Y., Mr. Kunz " has discovered 
a cave wl 
lose 
wall 
Is are lir 
led V 
vith crysi 
tals of sea-green ///^rv'/^, forming 
groups w 
eighi 
'^g 
from te 
n to 
several 
hundred pounds. Attached to 
the fluor 
per 
feet 
small n: 
tctrahe 
dral 
, Oi lithi 
vnargc. and imbedded in these 
of chakopyrite. A water-worn 
fragment 
of // 
're-( 
././/isn 
lentil 
:)ned by 
the same author as having been 
