’ 
208 
e2°-¢ yoy d ©b c - 
a. Alberese. b. Alberese with ae eee Gabbro rosso. 
d, Miocene? with alabaster. - e, e. Subapennine. 
mountain mass at Civita Castellina, Where it performs, as above 
mentioned, the part of an intrusive agént. It there throws off on 
its eastern summit the alberese limestowe in a highly fractured anc 
mineralized condition, as seen in fig. 3. From the natural section 
here exhibited, it is certain that this eruption of “ gabbro” took 
place after the consolidation of the alberese and macigno forma 
tions, 7. e. after the younger chalk and older eocene. It is also 
further evident that another movement of elevation occurred after 
the miocene period ; for not only is the limestone associated with 
white marls to a great extent loaded with alabaster, which some 
persons might infer was altered limestone, but the whole of thismass 
has been considered to be miocene, simply because it dips away 
from the alberese and gabbro in such inclined strata, and is thus 
placed in striking contrast with the subapennine or pliocene marls 
of the valley which surround a boss of “ gabbro rosso” in per- 
fectly horizontal and unbroken layers. The altered alberese at 
Civita Castellina has here and there serpentinous soft bands, and 
bears a metamorphic aspect, with a slickenside surface, accompa- 
nied by cracks and numerous veins of arragonite, all of which 
specially abound near the junction of the alberese- with the 
“‘gabbro.” Copper veins, however, either traverse the alberese or 
run down its junction with the gabbro ; and are therefore of date 
sterior to the eruption of the latter. It is indeed the opinion of 
illa, that the copper veins have resulted from ‘the same igneous 
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diversified in aspect and structure, seemed to me to form parts of 
the same eruptive matter which has penetr&ted the macigno and 
aie ee fale a 
