22 PROF. T. G. BONNET ON THE HORNBLENDIC AND OTHER 



clusters of opacite, associated with a colourless platy uniaxial or 

 orthorhombic mineral (the whole from '01 to '02 inch diameter), 

 may indicate the former presence of one or more of these; indeed, 

 so far as I can judge from the traces of cleavage-planes, I should 

 infer that a little enstatite, and possibly hornblende, had once been 

 present. The banding is less conspicuous under the microscope 

 than to the naked eye, but still is indicated by a general parallelism 

 of the longer " strings," forming the meshes of the network, by an 

 imperfect linear arrangement in the clustered granules of opacite, 

 and by slight differences in the colour and mineral structure of the 

 matrix, so that I regard it as a record of an original structure in 

 the rock-mass*. 



In one place, at the base of the cliff, the serpentine exhibits a 

 curious structure. Perpendicular to each joint-face cracks have 

 formed about an inch deep, which have been filled up with whitish 

 steatite, so as to exhibit a polygonal reticulation, the meshes being 

 about half an inch in diameter. A fracture- surface shows a border, 

 tolerably regular, of dull-coloured serpentine, divided by white 

 lines. The inner mass is sometimes traversed by bands about | 

 inch wide, with light edges and a dark inner stripe. 



I may add that, in the course of my work, I reexamined almost 

 all the junctions described in my former paper, and have no hesitation 

 in affirming that there is abundant proof of the intrusive character 

 of the serpentine in the Lizard district. Additional evidence, were 

 it needed, was obtained in a quarry at Ynys Head, north of Cadgwith, 

 where an exceptionally good section had been exposed, and in a 

 small mass of serpentine (not previously noticed) in the hornblende 

 schist to the north of Ugethawr, where the rotten serpentine is 

 readily distinguished from the other rock, which it has broken 

 through and disturbed. In short, I do not hesitate to say that if 

 we have any evidence on which we can rely as proving the intrusion 

 of an igneous into a sedimentary rock, we have it in the case of the 

 Lizard serpentine and the metamorphic series with which it is 

 associated. I mention this because some time since the following 

 remark with reference to my former paper appeared in an article 

 from the pen of Dr. Sterry Hunt, published in the (American) 

 ' Annual Record of Science' for 1878, p. 293: — "When it is con- 

 sidered that there is abundant evidence that the North-American 

 serpentines are indigenous, though often, like deposits of gypsum 

 and of iron-ore, in lenticular masses ; and, further, that the move- 

 ments which the ancient strata have suffered have produced great 

 crushings and displacements, it is not difficult to understand the 

 deceptive appearance of intrusion which these rocks exhibit, and 

 which are scarcely more remarkable than the accidents presented 

 by coal-seams in some disturbed and contorted areas." I content 

 * This is confirmed by the peculiarly compact condition of the serpentine in 

 the narrow dyke on the shore north of Kynance (last paper, p. 920), at the 

 junction at Ugethawr (ibid.), as well as in the cases described from Goonhilly 

 Down, so that in these places the peridotite was probably in a glassy or very 

 minutely crystalline condition (see Prof. Kenard's paper, " Peridotit von der 

 St. Paul's Insel im Atlantischen Ocean," Neues Jahrbuch fur Mineralogie, 1879). 



