GEOLOGICAL HISTORY OF SERPENTINES. 179 
gates in which an admixture of these with a feldspathic element marks a transition to the 
great group of rocks essentially made up of an anorthic feldspar with a pyroxenic element, 
(hornblende, pyroxene, enstatite, etc.,) including the so-called greenstones—diorites, diabases 
and euphotides—which are the frequent associates of serpentines. All of these rocks were 
embraced by Savi under the convenient though not scientifically-defined name of ophio- 
lites. 
40. The name of gabbro (from an Italian locality of these rocks, near Leghorn) was 
adopted and extended by Tozzetti, in the last century, in a similar sense. His numerous 
species of gabbro embraced serpentines, and the various diallagic, hornblendic and feldspa- 
thic rocks already noticed, of which the red gabbro, or gabbro rosso, seems but a locally dis- 
colored and partially decayed form. The name of gabbro has come, with many lithologists, 
to mean a diabase, but it is employed in such a very indefinite manner that it would be 
well if it were dropped altogether from use. * It is often made to include the granitone 
of the Tuscan stone-workers, the so-called euphotide, in which, as we are told. the feldspa- 
thic element is replaced by saussurite. Although this name is often given to a compact 
variety of triclinic feldspar, the true saussurite is, as I have elsewhere shown, a compact 
zoisite, distinguished from feldspar by its much greater density and hardness. The two 
minerals are, however, intimately associated in the euphotides alike of the Alps and the 
Apennines, as seen in specimens which I have examined both from Monte Rosa and from 
Monteferrato. + 
§ 41. The results of Bonney’s studies are given in a paper on Ligurian and Tuscan 
serpentines in the Geological Magazine for August, 1879. He therein records his observa- 
tions in different localities in these regions, which, for reasons to be made apparent farther 
on, we arrange in three geographical groups. First, ophiolites on the sea-coast west of 
Genoa, where Bonney describes the serpentines as occurring with dark-colored schists and 
gabbros, instancing among the mineral species found with them, pyroxene, hornblende, 
glaucophane, chlorite and saussurite. He states that the ophiolites of this region are so 
like those of Cornwall that he feels justified in claiming for them a similar origin. In a 
second group, he notices the ophiolites of a region immediately eastward of the first, 
between Genoa and Spezzia, which he describes as very similar to these. Bonney rejects 
for all of these serpentines, as for those of Cornwall, the notion that they have been formed 
by metasomatosis from diorite, diabase or hornblendic rocks, a hypothesis which he con- 
ceives tochave been founded on hasty and imperfect generalizations, and regards them as 
generated by the hydration of intruded olivine-rocks. In the third geographical group 
of the ophiolites described by Bonney, he places those of Monteferrato in Prato, near 
Florence. In each of these districts, he notices the close resemblances between the ophio- 
litic rocks and those met with in the similar areas in Great Britain, and supposes an 
intrusion of serpentine, or rather of olivine-rock, among crystalline schists, followed by a 
later intrusion of gabbro. He has no hesitation in assigning to the serpentines of these 
three districts similar conditions and origin to those in Cornwall, North Wales and Scot- 
land, remarking that notwithstanding the fact hat the Italian serpentines are, in part at 

* See in this connection, Cocchi, Bull. Soc. Géol. de Fr. (1856), xiii., 261; also his valuable memoir on the 
Igneous and Sedimentary Rocks of Tuscany, ibid, 1861, pp. 227-300. 
+ Contributions to the History of Euphotide and Saussurite. Amer. Jour. Science, 1858, xxv., 437, 
