. = 
Mineralogy and Geology. 269 
that it must arise from sulphate of magnesia being the agent by which 
the change into dolomite was produced. ‘The magnesia of the sul- 
phate of magnesia going to a portion of lime to form dolomite (or 
carbonate of lime and magnesia), the sulphuric acid thus set free woald 
form with water and another portion of the carbonate of lime, gyp- 
sum (sulphate of lime). 
ut chemistry had shown ‘that when a solution of gypsum was filter- 
ed through pulverized dolomite, sulphaté of magnesia was formed and 
carbonate of lime set free. Haidinger had also observed the tlatak: 
cence of sulphate of magnesia in yout quarries, and traced it toa 
decomposition of this character. As these last are results of ordinary 
exposure, Haidinger ios wat inferred that this ion requir ed 
no unusual heat or ew for the ee? pera (a 
dolomisation), both hea pete might 
ment is point were inetd | in 1848, b Markogel and Wahler, 
but were not carried out. Von ig) has at Cl Vane this ies and 
pote sage the view so far as t o show 8 of lime and 
ate of magnesia in the shi ste, zn Lang per ie lige 
ander pressure, dolomite is actually form d, together wit 
this dolomisation. roe SS usioniaa of our western states con- 
D. 
In the analysis of recent corals by »Prof. B. Silliman, Jr., published 
in the. volume on Zoophytes ‘by the writer, there is less than sone one per 
cent. of magnesia, But in a'‘eompact coral rock made up of material 
of coral origin, he found 38:07 per cent. of carbonate of magnesia. 
The coral rock was a result of consolidation without heat, as we may 
judge from the absence of all evidence of its effects. Another speci+ 
men of a fragmentary eharacter afforded 5-29 per cent. of magnesia. 
Both resemble the common reef rocks: They appear to show that 
there are circumstances in which the magnesian salt of the ocean, and 
the carbonate of Jimé of the coralsymay react and produce a magne- 
sian rock at the ordinary —— gS of the water. This ac- 
tion may favor the consolidation rock which.is in progress beneath 
rial, the more magnesian the product; this principle accounts for the 
1D. proportion of magnesiayin the sécond case alluded to above.— 
Dana, + 
5. Three Minerals from the Lake Sapueier ene Rexion. p by J. 
D. Wuirney, (Jour. Bost: Soc. Nat. Hist., v, 486.)—These esi 
occur at Kewenaw oo and on Isle Royal, where many zeolites 
been found. The first of the three analyzed and desseiiog by Mr. 
Whitney, is Tabular spar. ‘The other two are new species 
(1.) Jacksonite, (named in honor of Dr. C. T. Jewkedn:)* his near 
prehnite in composition, but contains no water. It occurs in finely ra~ 
diated or a radiated masses, of a white color tinged with er 
H.=6. G.= 2681. Translucent; lustre vitreous: Dissolves slowly 
but perfectly in muriatic acid, the silica separating as a flocky powder. 
Srconpv Senizs, Vol. VI, No. se 1848. 3 
