
GEOLOGICAL HISTORY OF SERPENTINES. 201 
of eocene limestones and shales, which, in some places, however, rest directly upon the 
ophiolite, or with the intervention only by a layer of comminuted serpentine-rock, described. 
by Capacci as an ophiolitic sand (arenaria ofiolitica.) These overlying strata have a general 
dip away from the serpentine, that is to say to the easward, of from 20° to 70°, but in some 
sections, as to the east and northeast of Figline, are represented in Capacci’s sections as 
nearly horizontal, with small undulations exposing, in valleys, the phthanite, and even the 
serpentine beneath the the alberese, 
§ 98. On the western side of the hill where, as already said, these eocene strata appear 
nearly up to the summit, and plunge beneath the ophiolite, their dip, as seen along the 
southwest border, is from 54 to 64 to the northeast. Here is observed a significant fact, 
which is shown in the sections of Capacci; namely, that the previously-noted relations of 
the serpentine, phthanite and alberese are reversed. While on the eastern slope these three 
rocks appear in the ascending order just named, we find on the opposite flank of the hill, 
in the ascending section, alberese, phthanite and serpentine; the serpentine overlying 
the phthanite, and the latter the alberese. The natural and obvious interpretation of these 
facts is that we have here simply an inversion of the natural order, resulting from an 
overturn of the strata on the western side of the hill. 
§ 99. The ophiolitic mass itself is not simple but, as described and figured by Capacci, 
is essentially composed of two layers of serpentine, with an intercalated lens of euphotide. 
Besides this rock, which has been the object of repeated studies, the last by Cossa, this 
lithologist has described associated masses of diabase, while Capacci has observed others of 
dioritic rocks, including a green variety distinguished as gab bro-verde, sometimes becoming 
variolitic, as well as the so-called gabbro-rosso, which, as there seen, is an iron-stained, 
somewhat calcareous dioritie rock, concretionary in structure, and apparently in a decom- 
posing state. 
§ 100. Capacci’s view of the relations of these various rocks to one another, and to the 
accompanying eocene strata, is in accordance with the hypothesis already set forth (§ 93). 
He regards the ophiolite of Monteferrato as a great lenticular or almond-shaped mass 
(un'amigdala ofiolitica), “intercalated in perfect concordance of stratification, among the 
strata of alberese and galestro of the eocene formation,” which have been subsequently 
tilted, so as to give to the whole series an eastward inclination. In accordance with this 
conception, he supposes that at a certain time during the accumulation of the eocene 
strata, there came, from a rupture in the earth’s crust, a sudden effusion of an aqueous 
magnesian magma, which was spread out beneath the sea, and was subsequently overlaid by 
a continuation of the eocene beds, as before. The silicious sediment constituting the phtha- 
nite which, on the west side, is seen to underlie the ophiolite is, in this view, a portion 
of previously deposited and altered shale, while the phthanite on the east side is another 
portion of a similar sediment, subsequently laid down upon the ophiolite. 
§ 101. The ophiolitic mass is thus, like all the other serpentines of Tuscany, of eocene 
age. The variousrocks which enter into its constitution appear in the form of “lenticular 
masses or almond-shaped concentrations,” of which the euphotide and the gabbros are 
examples. The gabbro-rosso is found in masses at the contact of the ophiolite with the 
phthanite, and results from the alteration of a diabasic rock by the action of thermal 
waters. These have also changed the galestro into the phthanite found both above and 
Sec. IV., 1883. 26, 
