GEOLOGY. 459 



to the evidence in favor of the apparently aqueous deposition of ser- 

 pentine rocks. 



In this connection should be mentioned the recent conclusions with 

 regard to the great deposits of olivine rock, once described as of igneous 

 and eruptive origin, but, from recent observations in many parts of the 

 globe, now coming to be regarded as a stratified indigenous rock. The 

 recent studies of Tornebohm, Brogger, and others of the olivine rocks of 

 Norway unite in showing it to be one of the stratified rocks of that re- 

 gion, where it is intercalated with other crystalline schists. A similar 

 conclusion was announced by the present writer, in 1879, with regard 

 to the bedded olivine rocks of North Carolina; while the recent studies in 

 Greece, by Diller, show that the olivine rock of Mount Ida. in the Troad, 

 passes into olivine-beariug talcose schists, and is associated with crys- 

 talline limestones and with other crystalline schists. Julieu has recently 

 discussed the olivine rocks of North Carolina, of which he recognizes the 

 sedimentary character and their interstratificatiou with hornblendic, tal- 

 cose, and chalcedonic rocks, which he supposes to result from the alter- 

 ation of the olivine ; but he* seeks for the origin of all this in beds of 

 olivine sand, for which he imagines an igneous source. Varieties of 

 olivine are known to be formed by igneous fusion, but its mode of oc- 

 currence in these and other crystalline schists, and in crystalline lime- 

 stones, is incompatible with such an origin, and only explicable on the 

 theory of its aqueous origin. 



This question assumes a curious geological importance in connection 

 with the hypothesis of the permanency of oceanic basins. The little 

 reefs which mr.ke up the islands of St. Paul are situated nearly under 

 the equator, in the mid-Atlantic, longitude 29° 2' west, and rise ab- 

 ruptly from 400 or 500 fathoms of water, which are found within one 

 and two miles of them. The rocks of which they consist have just 

 been examined by K6nard and found to consist of a common variety of 

 olivine rock, containing, besides this mineral, portions of actinolite, aud 

 a variety of pyroxene, with grains of chromite or picotite; the whole ar- 

 rangement of these elements resembling greatly the so-called gneissic 

 structure which characterizes certain crystalline schists. In a word, 

 the rock of St. Paul's has the characters of an Eozoic crystalline 

 schist rather than those of an eruptive rock. It has been suggested 

 that these little islands are the remaining summit of a submerged con- 

 tinental area, a vanished Atlantis, the mountain peaks of which were 

 of crystalline schists, a view to which Bernard inclines, and which co-in- 

 cides with the conclusions now deduced from the study of similar rocks in 

 Norway, in Greece, and in North America. The significance of the dis- 

 covery in mid-ocean of stratiform crystalline rocks like those of our 

 continental areas is obvious. 



SILICIOUS DEPOSITS. 



Sorby's microscopical observations in 1880 showed that in many sand- 

 stones there has been a deposit of silica in the form of quartz upon the 



