OF THE MOKE DISTURBED ZONES OF THE EARTH'S CRUST. 465 



developed in the particles, by their being heated to a point at which they could 

 begin to move among themselves, or upon their own axis, I have endeavoured 

 to show, that whether the cleavage-traversed strata have been much disturbed or 

 not, the cleavage planes invariably approximate to parallelism with those great 

 planes in the crust, which appear to have been the planes of maximum temperature. 

 It has been already stated in the present paper, that the cleavage dip is parallel 

 to the average dip of the anticlinal and synclinal axis planes, or those bisecting 

 the flexures. Now, it is easy to prove, that these axis planes, and the inverted 

 parts of the flexures, are just those portions where the greatest wrenching, Assur- 

 ing, and opening of the strata must have occurred, and where the highly-heated, 

 pent up, volcanic steam and gases, and liquid mineral matter, must have found 

 their chief channels upwards to the surface. 



Without attempting at present to apply this doctrine in detail, I will content 

 myself with reviving a suggestion I formerly put forth, that every plicated belt of 

 strata may be looked upon as having, from the causes here adverted to, become 

 traversed at the time of their folding and metamorphism, by a series of alternate 

 hotter and cooler parallel planes or zones of temperature, arranged in oblique dip, 

 coincident approximately with the axis planes of the flexures. These planes or 

 surfaces of high temperature, we may suppose to have acted to polarize the par- 

 ticles in corresponding planes, by transmitting through the half-softened mass, a 

 succession of parallel waves of heat, stimulating the molecular crystallizing forces, 

 which are ever resident in mineral matter, and which only await there the quicken- 

 ing influence of such a temperature, to develop in the mass special lines and 

 surfaces of maximum and minimum cohesion. 



This conception, that the surfaces or planes of crystalline lamination, includ- 

 ing cleavage, which is but a lower grade of the same species of molecular meta- 

 morphism, are approximately parallel to the surfaces of the waves of temperature, 

 which have moved through the strata, is not a mere hypothetical speculation, 

 but an induction at which I have arrived, from a comparison of many obser- 

 vations of my own, with phenomena well recorded by the ablest geologists. 

 Nearly all observers who have noted the influence of igneous dykes and veins 

 upon the strata adjoining them, both in mines and external exposures, have seen 

 a more or less distinct lamination or cleavage adjoining the walls of the once 

 heated mineral matter, and have been struck by its very general parallelism, to 

 the surface or the axis of the vein. Cases occur in strata of all ages, and are 

 frequently brought to light in coal-fields, when nearly vertical dykes cutting low 

 dipping or horizontal shales, susceptible of the cleavage metamorphism, have 

 occasioned in the latter a true cleavage perpendicular to the stratification, or 

 parallel, more strictly speaking, with the once hot surface of the intrusive 

 rock. 



