92 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



go, they thus most completely bear out the prevalent theory of the 

 true metamorphic origin of schists ; but, at the same time, the spe- 

 cimens which I have examined have been too exclusively derived 

 from particular districts to warrant my extending this conclusion 

 to all rocks of similar general character in other localities, or of 

 earlier epoch than those of the central Highlands of Scotland. 

 A much more extended inquiry would be necessary. But I am fully 

 convinced that the true nature of all such rocks could be learned 

 by the further application of the methods now described. 



Conclusion. 



It will thus be seen that my aim has been to trace the origin 

 of the material of stratified rocks, and afterwards to study the 

 various mechanical and chemical changes to which it has been sub- 

 jected, and thus to show the connexion between modern mud and 

 our oldest schistose rocks. In some cases there has been a com- 

 plete cycle, the material having been derived from crystalliue rocks, 

 then deposited mechanically, and finally reconverted into crys- 

 talline rocks. In thus dealing with such a wide subject, as a whole, 

 I have been led to treat some questions in a manner which may 

 appear rather unusual, but, as I believe, not on that account less 

 correctly. I cannot but feel how much of the detail still remains 

 unknown ; and probably when known it will be found necessary 

 to modify some of my general conclusions. We often meet with 

 two or more structures, each clearly enough due to different causes, 

 and many of such an intermediate character that it is extremely 

 difficult to form a just estimate of the relative influence of the 

 various causes which have probably conspired to produce the 

 result. This and other unavoidable difficulties necessarily make 

 such a first attempt somewhat imperfect ; yet I trust that what 

 I have said may, at all events, serve in some measure to point 

 out what may be done.; and to lead others to investigate the subject 

 more completely. Considering the very wide range of subjects 

 which I have been compelled to examine from a more or less 

 novel point of view, it is satisfactory to find that in most cases 

 the new facts tend only to remove doubts, and seldom, if ever, 

 do more than slightly modify the conclusions arrived at by geolo- 

 gists from the consideration of totally different and independent 

 evidence. 



