374 On some Relations of the Salts of Lime and Magnesia, 
57. Magnesian limestones containing an excess of carbonate 
of magnesia are not uncommon; one from the muschelkalk of 
Thuringia gave to Senft, carbonate of lime 42°9, carbonate o 
magnesia 55°4, besides 2°7 of carbonate of iron =101°0. A la- 
. 
custrine dolomite from the brown-coal formation near Giessen 
assic system in Germany. A tender greenish schistose marl 
from Tubingen effervesced very slightly with acids, and gave 
for 100-00 parts, carbonate of lime 14°56, carbonate of magnesia 
19°10, the remainder being clay with a little iron-oxyd. (Senft, 
‘BB, « 
83-94, carbonate of lime 0°67, with 10°81 of clay, water, ete. 
(L. and K. Jahresbericht, 1849, 581.) 
58. Magnesian rocks allied to the last occur in the Hudson 
River group of eastern Canada, and were described by me sev- 
eral years since. In the township of Sutton, interstratified with 
dolomite, steatite and taleo-quartzose strata, is a bed of green 
and white reddish-weathering crystalline rock, gneissoid in struc- 
ture, and containing variable porportions of magnesian carbon- 
such rocks correctly ascribes the origin of the deposits of peroxyd of manganese 
met with in that region. Beds of silicate of manganese, more or less intermingled 
rusted in part with erystalline peroxyd of manganese. Acids in the cold searcely 
attack this mineral, but h nhisie and dissolves it with effervescence, leaving 
residue of 14-4 pee of silica, of which the greater part is soluble in a dilute alka- 
line solution. The analysis gave me besides 84°6 p.c. of carbonate of manganese, 
i magnesia, ( 
Cee eee ire 
