SCROPE OX INTERNAL STRUCTURE OF GNEISSIC ROCKS. 367 



tlie fusion and rc-coiiSoliJation in a crystalline state of sedimentarj 

 strata, is a theovy not iiere called in question. iLy suggestion only 

 amounts to this, that their foliation does not represent the original 

 sedimentary bedding, but was brought about by the internal friction of 

 their already crystallized particles during protrusion or elevation, under 

 circumstances of intense pressure and lateral motion in opposite or 

 nearly opposite directions. 



It is not inconsistent with, this view to admit that a certain amount 

 of crystallization may have accompanied or followed these internal 

 movements. For it is known that some freedom of motion is necessary 

 to the exercise of the crystallific action, and also that the atomic 

 particles must be brought within certain small distances. l^Tow, during 

 the internal movements to which I have referred, some of the dis- 

 aggregated mineral elements may be brought so close together as to 

 cause crystallization to take place. And thus new and even large 

 crystals may be formed in the midst of granular or amorphous matter. 

 In many of the crystalline schists, as well as in some clinkstone and 

 felspar porphyries, we find lengthened crystals whose acicular and 

 delicate, but unbroken, form renders it difficult to suppose them to 

 have undergone, since their production, any great amount of friction. 

 If we suppose these to have crystallized while the mass of which they 

 form part was subjected to a certain amount of motion under intense 

 pressure, it will be obvious that their major axes should be found (as I 

 believe they invariably are) in planes more or less perpendicular to the 

 direction of the pressure, and corresponding to that of the movement 

 (as indicated by the foliation of the rock), since the mobility necessary 

 to the crystallific action will have been freest in that direction. 

 . I may remark that the influence of internal friction, caused by 

 movements under extreme and irregular pressure, must be equally 

 operative in the case of rocks of aqueous as in those of igneous origin — 

 of shales, limestones, and grits, as well as of granites or trachytes, under 

 similar circumstances of imperfect liquidity, irrespective of change of 

 temperature. 



There is every reason to believe that many of the sedimentary strata 

 were, at the time of their elevation above the levels at which they were 

 deposited, in a more or less soft and semi-liquid condition, permeated 

 with water, and consequently liable to much internal and irregular 

 movement among their solid particles, under the action of the enormous 



