1856.] SCROPE CRATERS AND LAVAS. 345 



Their exact comformity with those which were first developed in my 

 treatise on Volcanos, published 1824-25, and repeated in the Preface 

 to my volume on Central France in 1826-27, will be evident to any 

 one who will take the trouble to refer to those works. 



It is not, however, for the vain purpose of claiming a priority in 

 these views, that I now ask the attention of the Society to them, but 

 because the subject has not, I think, yet attained the consideration 

 it deserves from the geologists of this country ; and especially because 

 of its leading, if followed out, to further inferences of considerable 

 importance, which were likewise suggested by me in 1825, but have 

 been hitherto only partially pursued to their legitimate consequences. 



Laminated or schistose rocks, slaty cleavage, and folded rocks. — 

 I refer to the mechanical changes in the texture and structure 

 of the plutonic rocks which could not fail to have resulted from the 

 mutual friction of the component crystalline particles attendant on 

 their internal movements, whether caused by mere dilatation and 

 re-compression in place, or by a shifting of the entire mass in any 

 direction, under intense and opposite, but irregular pressures. 



I was led to reflect on this by observation of the ribboned pitch- 

 stones of Ponza and Ischia, in which, while in a state of vitreous 

 fusion, crystallites had formed (just like those of the Oldbury ob- 

 sidian), and subsequently been ijroken up by the movement of the 

 semi-liquid mass, and drawn out into long stripes, giving a ribboned 

 appearance to the rock. 



Further examination proved to me that the ribboned trachytes of 

 Ponza and Ischia, and some ribboned clinkstones, owed that character 

 to a similar elongation of the felspar crystals and felspathic particles 

 which they previously contained, in the direction in which the semi- 

 liquid mass flowed, or rather was forced to move, and in which the 

 pores or cells, when there are any, are equally elongated. These 

 observations suggested to my mind the reflection that the solid 

 particles of any crystalline rock which is put in motion while in a 

 state of imperfect solidity, and under the influence, of opposing 

 pressures, must be subject to a great amount of mutual friction or 

 disturbance, by which their final arrangement when wholly consoli- 

 dated will be determined. 



Thus suppose a mass of granite, of which A B (fig. 4) represents 



Fig. 5. 



H 



the section, consisting of crystals of felspar and mica irregularly dis- 

 posed in a basis of more or less liquefied or gelatinous silex, exposed 



