178 DR. THOMAS STERRY HUNT ON THE 
The hypothesis of the igneous and eruptive origin of serpentine is well illus- 
trated in the paper by Prof. Bonney on the serpentines of Cornwall, England, in the Quar- 
terly Geological Journal for November, 1877, supplemented by his later observations on 
the geology of that region, communicated to the Geological Society of London in Novem- 
ber, 1882, and published in abstract in the Geological Magazine for December, 1882 ; in 
which connection should also be consulted his paper on Ligurian and Tuscan serpentines 
in the same magazine for August, 1879. 
§ 37. Bonney at first accepted the then generally received opinion that the erystalline 
schists in which the serpentines of Cornwall are included, are altered paleozoic, but in his 
latest studies of the region he announces the conclusion that they are not paleozoic, but 
eozoic (archæan) and consist of a great series, divided into three groups. The lower one, 
of greenish micaceous and hornblendic schists, he compares with those of Holyhead 
Anglesea, and the adjacent shores of the Menai strait, in Wales. The rocks of these localities, 
belonging to the Pebidian series of Hicks, have been examined by the present writer, and, 
by him compared with the Huronian of North America. * 
§ 38. Above these greenish schists, in Cornwall, according to Bonney, is a black horn- 
blendic group, and a still higher granulitic group with granitic bands; the characters of 
these two recalling portions of the Montalban or upper gnessic series of North America and 
of the Alps. It is in the lowest of these three divisions, consisting chiefly of micaceous 
and hornblendic schists, that the Cornish serpentines appear, accompanied by so- 
called gabbros or greenstones. Bonney finds, with Boase and with De la Beche, examples of 
apparent interstratification and passage between these rocks and the schists, but concludes 
nevertheless, that there is evidence that the serpentine was introduced after the crystalli- 
zation of these, and that its eruption was followed by that of gabbros of two dates, and 
subsequently by that of granitic and dark-colored trappean rocks. He throws doubt 
upon the ancient hypothesis of the conversion of hornblendic and pyroxenic rocks into ser- 
pentine, and supposes this mineral species to have resulted from the hydration of an 
olivine-rock, such as lherzolite, which consists essentially of olivine with enstatite ; grains 
of both of which species may be detected by the microscope in thin sections of some of 
the Cornish serpentines. According to John Arthur Phillips, some of so-called greenstones 
of Cornwall are eruptive, while others are undoubtedly indigenous, and graduate into the 
crystalline schists of the region. Respecting these, the writer said in 1878, “these bedded 
greenstones, with their associated crystalline schists, appear to have strong resemblances to 
the rocks of the Huronian series, to which farther study will probably show them to 
belong.” + 
§ 39. Bonney has also extended his observations to the serpentines and associated rocks 
in Italy, which he includes under the general title of ophiolites. This name, and the ~ 
kindred one of ophites (Greek, ophites, a serpent), alluding to their greenish colour, resem- 
bling that of the skins of some serpents, has been extended so as to include both true ser- 
pentine, and the frequently associated rocks which present some analogies with it in color. 
In fact, we pass from pure serpentine, and admixtures of this with carbonates, to serpen- 
tinic rocks including more or less of diallage, bronzite or bastite, and thence to aggre- 

* Amer. Jour. Science, 1880, vol. xix, pp. 276, 281. 
+ Harpers’ Annual Record for 1878, page 308, 

