184 OUTLINES OF FIELD-GEOLOGY PART I 



rocks are metamorphosed sediments may lose 



all reliable evidence of their bedding and consequently of 

 their order of succession, and then the foliation-planes, 

 no matter how distinct and persistent, can afford no 

 trustworthy clue to the original sequence and structure 

 of the schists. In other areas the structure of the rocks 

 is so entirely crystalline, and the absence of any sign of 

 sedimentary origin in the rocks is so complete, that we 

 must seek for some other explanation of their banded 

 structure than that which would account for it by regard- 

 ing it as bedding. 



Foliated rocks are commonly crumpled and puckered 

 on a minute scale, as well as plicated on a large scale. 

 Sometimes they appear to be ranged vertically, like books 

 in a library. But a broad tract of bedded rocks set 

 on end, must often mean, as we have already seen, that 

 they have been folded upon themselves, and that the tops 

 of the folds have been cut away. (See p. 151, Fig. 49). 

 In fact, they may be so rapidly and constantly repeated, 

 that though placed on end, a comparatively small thick- 

 ness of strata may be made to cover a wide space, and 

 thus an effect may be produced somewhat like that which 

 would arise if they were approximately horizontal. 



If it is difficult to follow out the structure of a crumpled 

 region of ordinary sedimentary rocks, it is tenfold more 

 arduous to make progress in one of the crystalline schists. 

 The observer, however, may do much by making 

 numerous and careful observations of the direction and 

 angle of dip, where he finds that the folia are not vertical, 

 and has reason to suspect that they mark original bedding. 

 In this way, he may detect lines of anticlinal and synclinal 



