210 DR. THOMAS STERRY HUNT ON THE 
serpentine, and those containing the pure magnesian olivine, forsterite, are very close, 
and their relations indicate for all of them a common neptunian origin. 
$ 123. We pass from the olivine-bearing limestones to those rocks composed chiefly of 
olivine, which have received the names of dunite and lherzolite, and appear to be indi- 
genous interstratified masses. Such was my conclusion after examining them in North 
Carolina, in strata referred by me to the Montalban series, regarding which I wrote in 
1879: “Noticeable among the basic members of the terrane is the granular olivine or 
chrysolite-rock which, often accompanied by enstatite and by serpentine, appears to be 
interstratified in the micaceous and homblendic schists of the Montalban in North Caro- 
lina and in Georgia.” * Olivine-rocks, similar to those of North Carolina, have been 
observed among the crystalline schists in the province of Quebec, on the south side of the 
Gulf of St. Lawrence, but have not yet been carefully examined. 
§ 124. The typical lherzolite from the eastern Pyrennees, described by Zirkel, has since 
been studied by Bonney, who in 1877 + described the rock and its locality. It forms 
several masses of considerable size, near Vicdessos (Ariége), and is in contact with a sac- 
charoidal limestone, in which occur broad tongue-like portions of the lherzolite. This 
rock consists of olivine with admixtures of enstatite, diopside and picotite (a chromiferous 
spinel), the constituent minerals showing in their arrangement on weathered surfaces a 
“linear structure,” suggesting “an internal parallelism,” which Bonney, who looks upon 
the rocks as “igneous,” regards as due to movements of flow. The rock varies from 
coarsely to finely granular in texture, and includes in some cases a serpentinic mineral in 
its joints. The dunite of New Zealand, in specimens before me, presents in the arrange- 
ment of the contained chromite, a well-defined gneissic structure. 
§ 125. Similar rocks are found in N orway, specimens of which from Tafiord, received 
by the writer in 1878 from Prof. Kjerulf, were micaceous, and showed an evidently 
gneissoid structure. These rocks, consisting essentially of olivine, holding enstatite, 
diopside, chromite and a greyish mica, are found interstratified in gneiss, with quartzites 
and mica-schists, sometimes garnetiferous. From their late studies of this rock in various 
Norwegian localities, Tornebohm, Reusch, and Brégger agree that it must be classed 
among the crystalline schists, a judgment in which Rosenbusch concurs. The reasons for 
this conclusion, as set forth by Brégger, are briefly as follows: First, the invariably lam- 
inated structure of the olivine-rock, which is conformable to that of the enclosing 
gneiss ; and, second, the variations in the composition of the rock itself, as seen in adjacent 
layers. f With these gneissoid olivine-rocks of Norway may be compared the olivine 
known as glinkite, found in nodules in a talcose schist in the Urals, and also the schists 
lately described from Mount Ida in Greece. § In these, the transition is seen from true 
talc-schists to tale-schists containing more or less olivine, with pyroxene, and finally to 
massive olivine-rock ; the whole being associated with other crystalline schists and with 
limestones. The obyious conclusion from all the above facts is that no argument in favor of 
the igneous origin of serpentine can be drawn from its supposed derivation from olivine- 
rocks, since these are themselves, for the greater part, of neptunian origin. 

* Macfarlane’s Geological Hand-book, page 13. 
+ Geological Magazine, Feb. 1877. 
t Neues Jahrbuch fur Mineralogie, 1880, i., pp. 187, 195, 197. 
@ Science, Aug. 31, 1883, p. 255. 

