204 DR. THOMAS STERRY HUNT ON THE 
observations at this point served to strengthen my conviction that the ophiolite of Monte: 
ferrato is also but a small protruding mass of the same series. 
I was enabled subsequently, as already noticed, (§ 54) to examine with Signor Quin- 
tino Nella a portion of the ophiolitic series of admited eozoic age, as seen in the Biellese, 
in the province of Novara, and to confirm the judgments of Gastaldi, Cossa, Bonney and 
others as to the apparent identity of these ancient ophiolites with those found in 
Eastern Liguria. 
§ 107. We have already described, in a former part of this paper, the mass of eozoic 
serpentine which, in Staten Island, New York, rises from out of the horizontal or gently 
inclined cretaceous and triassic strata that have been deposited around its base. If now 
we conceive this region to be subjected to such movements as those which, along the 
eozoic belt a little further south, have compressed the Primal and Auroral strata against 
the northwest base of the South Mountain, and given them a southeast dip, we should 
have a phenomenon not unlike that presented by Monteferrato ; that is to say, a lenticular 
mass of ancient serpentine rising along the outcrop of southeastward-dipping mesozoic 
rocks, and differing only by the accidental circumstance that these, on the two sides, belong 
to different mesozoic horizons (22, 23.) 
VI—TuHE GENESIS OF SERPENTINES. 
§ 108. As regards the origin of the serpentine-rocks, we have already noticed briefly 
some of the hypotheses which have been proposed. Although those which suppose it to 
be derived by metasomatic changes from aluminous or calcareous rocks, either exotic or 
indigenous, such as granites, diabases, granulites or limestones, may be considered as now 
nearly obsolete, it may not be amiss to recall the fact that they represent two distinct and 
opposite schools, which agree only in admitting an unlimited alteration or change of 
substance in previously-formed rocks, through aqueous agencies. 
The first view, which may be described as a general metasomatic hypothesis adapted 
to plutonism, is that which derives not only serpentine but limestone from ordinary 
types of feldspathic rocks, such as granites, granulites, gneisses, diabases, and diorites. 
The integral conversion of all of these into serpentine by the complete elimination of the 
alumina, alkalies and lime, and the replacement of these bases by magnesia, has been 
maintained by many writers of repute belonging to the school in question. * 
§ 109. Others still have supposed that the same rocks might be changed into limestone, 
by a complete removal of the silica, also, and the substitution of carbonate of lime. This 
extreme view has found its boldest and most consistent advocates in Messrs. King and 
Rowney, who not only assert this origin for the limestone-masses found in the gneisses of 
Sweden and the Hebrides, but imagine that the bedded crystalline limestones, many 

* Bonney, who maintains the origin of serpentines by the hydration of eruptive olivine-rocks, has, in his 
paper already cited, given many reasons for rejecting the notion of the formation of serpentines by metasomatosis 
from the basic feldspathic rocks so ofteu associated therewith. The observed relations of the two are, in his 
opinion, wholly opposed to this view, and he insists upon the difficulty of conceiving that such a process of change 
should be limited to certain parts of a great mass, while leaving adjacent portions unaltered. From their distinet- 
ness, he is even led to the conclusion that the serpentines and their accompanying euphotides and diorites belong 
to successive periods of eruption. 

