GEOLOGICAL HISTORY OF SERPENTINES. 207 
§ 116. The conclusions of Dieulefait, as to the sedimentary character of the serpen- 
tines of Corsica, have already been mentioned (§ 71). He rejects the plittonic hypothesis 
of the origin of serpentines for the following reasons: The frequent alternation of 
very thin beds of serpentine with others of schists and of limestone equally thin; the 
changes in the constitution and composition of the serpentinic layers; these, being in 
one place pure serpentine, become gradually mingled with carbonate of lime, which at 
length constitutes a large proportion of the rock, and also forms lenticular masses in the 
midst of the calcareous serpentines. To all these, which are common to the serpentines 
of North America, we may add, as noted elsewhere, the frequent occurrence of grains, 
nodules, layers or lenticular masses of serpentine in beds of crystalline limestone. 
Dieulefait notes, moreover, the absence of any signs of igneous action at the contact 
between the serpentines and the underlying schists. He next adverts to the hydro- 
plutonic hypothesis, and pertinently asks on what grounds we are authorized to suppose 
the ejection of muds of magnesian silicate from the earth’s interior. 
§ 116. His own conclusion is that while these serpentines are sedimentary rocks in 
the most complete acceptation of the term, the mud or sediment which gave rise to them 
was not ejected from below, but was formed in estuaries of the sea, by reactions between 
the silicious matters derived from the decay of pre-existing rocks and the magnesian salts 
of the sea-water ; in which connection he insists upon the frequent metalliferous impreg- 
nations of the serpentines, as derived in like manner from the older rocks. This view of 
Dieulefait’s, set forth in 1880,* is, as Lotti remarks, no other than “the hypothesis enun- 
ciated by Sterry Hunt,” twenty years earlier. Lotti, for his part, while still reserving 
himself on the question of the supposed tertiary serpentines of Italy, adds, after his own 
studies of those of Corsica: “In any case, it is impossible, as Dieulefait has said, to 
regard the phenomena offered by these ancient serpentines as due to eruptions either of 
igneous or hydroplutonic magmas. The serpentine has either been deposited as such, as 
maintained by Sterry Hunt, and by Dieulefait, or is a sedimentary rock subsequently 
altered.” + We shall notice later on the views of Stapff on this subject. 
§ 117. The masses of rock known as serpentine are far from homogeneous in compo- 
sition. Apart from the admixtures of carbonate of lime, dolomite and magnesian carbonate, 
which often enter into their composition, they occasionally include besides the hydrated 
silicate, serpentine, the anhydrous species, olivine and enstatite or bronzite, and more 
rarely the hydrous species, tale ; silicates differing widely in density, in chemical stability, 
and in the oxygen-ratios between the silica and the fixed bases; that for olivine being 
1:1, for enstatite 2:1, for tale approximately 3:1, and for serpentine 4: 3. These differ- 
ences, in the hypothesis of the aqueous origin of serpentine, may well depend upon varia- 
tions in the composition of the generating soluble silicates, and upon the balance of 
affinities between silicic and carbonic acids in the watery menstruum, rather than upon 
the subsequent transformation of one magnesian silicate to another by addition or elimina- 
tion of silica or magnesia. The association, in the same mass, of anhydrous olivine with 
serpentine is generally regarded as evidence of the change of olivine into serpentine ; but, 
while admitting the conversion, under certain conditions, of both enstatite and olivine into 

* Comptes Rendus de l’Acad. des Sciences, xci. 1000. 
+ Lotti, Appunti Geologici sulla Corsica ; Boll. R. Comitato Geologico, anno 1883. 
