REPORT ON THE PETROLOGY OF THE ROCKS OF ST. PAUL. 15 



endeavoured to show in the figure, has undergone a remarkable process of folding, or 

 curling back upon itself. This crystal seems to have been partially softened, and to 

 have lain with its principal axis at right angles to the bands. It looks as if a current 

 had drawn along and bent into the shape of a U the fine lamellae of which the crystal 

 is composed, while allowing them to preserve their parallelism. The lamellae are frac- 

 tured at the summit of the arch of curve ; the edges of the fracture correspond exactly, 

 and the space between them is filled up with the ground-mass of the rock. The bands 

 of this ground-mass undulate around the broken crystal. The somewhat rounded frag- 

 ment of enstatite shown on the left hand side of fig. 2, near the top, in which the striae 

 appear to correspond with those of the folded crystal is, I think, a fragment of the latter. 1 



But sections presenting the same appearance may be found abundantly in the family 

 of the schists, to which, as the considerations adduced at the end of this report will show, 

 some of the peridotites should be referred. Among the analogies of microscopic structure 

 between true schists and the Rocks of St. Paul may be enumerated the ellipsoidal form of 

 the crystals, to which we have drawn attention, their entwinement by the bands in the 

 fundamental mass, the disruption of the larger individuals, as well as their curvature and 

 folding. The ill-defined ellipsoidal form of the olivine and enstatite of St. Paul's rock, 

 together with the ribbon structure, remind one forcibly of the folia of phyllitous substances 

 among the schist, with their ellipsoidal sections of quartz or of felspar, sometimes 

 rounded, sometimes in lines, and frequently ruptured. That gneissic structure recalls 

 the disposition of the undulated lines of the obsidians. Moreover, the schists frequently 

 show curved and folded crystals welded together by the encircling mass, as, for example, 

 the tourmaline of certain chloritic-schists, and the felspars of the porphyroids, whose 

 characters no one would now explain by the fluxion-structure. 



Undue stress should not be laid on the absence of a vitreous base as a proof that 

 the St. Paul's rock is not eruptive. I am well aware that the presence of amorphous and 

 isotropic matter is not an infallible indication of the igneous origin of a rock ; for such 

 matter has been detected even in schists. We therefore arrive at the conclusion that 

 the recognition of this special structure is not in itself sufficient to decide the question of 

 origin, which must be determined from a wider basis of evidence, as will be more fully 

 stated in a later part of this report. 2 



1 It may be remarked, however, that macroscopic crystals of bronzite are often bent and folded. They affect that 

 disposition naturally. In the preparations of the peridotic rocks of Greece described by Becke, and which I have had 

 occasion to examine, I have observed deformations analogous to those noted here. Becke says they are produced by 

 mechanical action. 



- At the time when I was studying this rock, I communicated the preliminary results, by letter, to Professor 

 Eosenbusch, and it was published by hi in the Neues Jahrbuch fur Min., 1879. In that preliminary communication I 

 expressed a much more decided opinion upon the existence of true fluxion-structure, and the most eminent lithologists to 

 whom I had shown the preparation (fig. 2) did not hesitate in declaring that this interpretation was well founded. If I 

 now express myself with more reserve, it is because recent researches tend more and more to establish the fact that in many 

 cases peridotites are rocks imbedded in the schisto- crystalline series with which they must have a common origin. 



