SCARBA. GEOLOGY. 



The accompanying figure will illustrate this appearance 

 better than any description.* In these instances the 

 contortions put on various appearances ; sometimes ex- 

 tremely intricate, but not very difficult of explanation. 

 In the greater number, the slate appears to be bent and 

 elongated, while the accompanying quartz rock is broken : 

 there is consequently a want of correspondence between 

 the two substances where the contortions take place ; al- 

 though in their immediate continuations, where undis- 

 turbed, they preserve an uniform parallel alternation. It 

 is probable that at the time when these changes were 

 effected, the quartz rock was perfectly indurated ; while 

 the slate was in that state of softness resembling moist 

 clay, which it appears in many cases to have retained long 

 after the period of its deposition. This opinion is con- 

 firmed by considering the different nature of these two 

 rocks. Whether the former is a mere aggregate of 

 particles previously crystallized, or a compound of such 

 particles united by a crystallized cement of quartz, it 

 could scarcely have existed in a very flexible state. Ac- 

 cordingly, it rarely presents instances of flexure, and even 

 these, where they occur, are trifling when compared with 

 those which are so frequent in the other primary strata. 

 Many of these latter substances have unquestionably been 

 deposited from water, either in the state of very fine pow- 

 der, or of extremely minute fragments ; while in some 

 instances, and particularly in the case of limestone, a 

 process of crystallization has either taken place in the 

 deposited mass, or has proceeded simultaneously with the 

 precipitation of the earthy matters. The quantity of water 

 which substances in this state are known to hold, and 

 which in the case of deposits of clay in particular, is so 

 remarkable, will explain their power of retaining a certain 

 degree of flexibility, or, in some instances, even an abso- 

 lute ductility, lono after they have assumed the external 



* Plate XI. tig. 4. 



