= 
224 T. 8. Hunt on Ophiolites. 
A portion of the powder of this last specimen of the con- 
glomerate was ignited for ten minutes over a spirit-lamp, and 
then boiled with a solution of nitrate of ammonia, so long asa 
erceptible odor of ammonia was evolved; there were dissolved 
y this means 6°50 per cent of carbonate of lime, and 7°65 of 
carbonate of magnesia. 
Veins of from four to six lines in breadth are often met with 
in this conglomerate. Their walls are covered with a thin layer 
of pale green serpentine, having a fibrous structtre perpendicu- 
lar to the sides of the vein; upon this is deposited a bluish-white 
fine grained dolomite, while in the middle a nearly pure cleava- 
ble calcite occurs. The analysis of a portion of this dolomite 
gave :— 
Carbonate of lime, - - - : - - 59:32 
“ “ magnesia, “ = . - 84:15 
a ©. 300, 1 = - - - - - 4°83 
98°30 
would however be ee without the description of another 
marble of Roxbury in that state; it has been examined by ¥™ 
©. T. Jackson and Dr. A. A. Hayes of Boston. 
. Jackson (this Journal, [2], vol. xxiii, p. 125,) peg 
“tion of 
‘ ,) su 
I separating from the rock a mineral having the compos 
rbonate 
of magnesia, and others of ferriferous dolomite, whic tra 9) 
the mass. According to Dr. Hayes, (ibid, [2], vol. xx1, P a 
the rock is an aggregate of fibrous and compact asbestus, Oe 
and argillite, the whole cemented by carbonate of magnest® 
which forms according to him, on an average, 38 p. ©. 4 
mass. He has also shown that the ophiolites of Cavendish, 
of Lynnfield in the same region, contain carbonate of a 
without any lime. Through the kindness of the above? 
By, ae | 
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