184 T. S. Hunt on Lithology. 
dissolved the carbonate of lime, and left a residue, the analyses 
of which, from two different portions of the rock, are given 
d 
under III. and Iv. 
Perey Se eee Sse Oe 
Alumina, - - - - 1831 
Lime, - * * - = 93 
Wacoal, 36 st 8 87 
Protoxyd of iron, - - - 
Potash, - - - - 5:55 
Soda, Siege ee eS = "89 
Volatile, - - - - ase 
99°57 
5°27 417 
3°60 46 
314 undet 
1:22 ve 
90 1:20 
98-77 98:04 
95°02 
The residue from the unaltered limestone, including the silica 
soluble in alkalies, contains nearly 75°5 hundredths of silica, and 
165 of alumina. These, in the vicinity of the 
olerite, have 
become saturated with protoxyd bases, including the small por- 
tions of magnesia and of oxyd of iron which the limestone eon- 
tains, This process evidently involves a decomposition of the 
carbonate of lime, and the expulsion of the carbonic acid. It 
is worthy of remark that while the unaltered limestone contains 
a little carbonate of! magnesia, the rock from which 111. was ob- 
5 
oN 
sen 
S 
oO 
Qu 
p 
3 
be] 
| 
Q 
o 
° 
Leary 
5 
pS) 
dQ 
5 
a 
r 
co 
3 
ro 
sot 
= 
far) 
S) 
5 
fe) 
8 
a 
po 
marks an intermediate stage in the process, and shows moreover 
that the alkalies are still retained in combination with the alu- 
minous silicate. These amorphous silicates, which have been 
formed by local metamorphism, might, under favorable circum- 
stances, have crystallized in the forms of feldspar, scapolite, gat- 
net, pyroxene, or some other of the silicious minerals which 80 
n occur in metamorphic limestones, The agent in producing 
these silicates of protoxyds at the expense of the carbonates 
the limestone, was Hearn a portion of alkaline salt, either de- 
rived from the fel 
infil 
spathic matter of the limestone, or possibly 
trated from the contiguous feldspathic rock; whose elevated 
temperature produced the reaction which has resulted in thus 
altering this limesto: 
ne. 
Similar examples of local alteration are met with in several 
other places near to the intrusive rocks of the Montreal group- 
The schists of the Utica formation in contact with a dike of 1n- 
ass of tra- 
h dark-green cleavable hornblende, which 
i ler cases encloses small ded 
bier 
omite. (See for a description: and analyses of 
Silos p. 634.) sa 
