The Devonian MetamorpMc Rochs. 27 



relations of the crystalline rocks of Salcombe to the Lower Devonian 

 rocks on their northern margin. As remarked in the preface by the 

 Director of the Survey, " the age of the schists is left undecided by 

 the author, though more definite views on the subject have been 

 expressed in favour of their antiquity by Professor Bonney and 

 Miss Kaisin, and in favour of their being metamorphosed Devonian 

 rocks by Jukes & Holl, A. Somervail, and A. E. Hunt." 



It may well be supposed that there has been an extensive 

 literature on this subject, and on p. 42 a summary of the principal 

 works is given. Commencing with De la Beche, the father of the 

 Geological Survey, our author observes that he approaches the 

 subject with characteristic caution. There appears to have been 

 a belief in some quarters that De la Beche favoured the notion that 

 the Metamorphic schists were altered Devonian rocks. Yet his views 

 as enunciated in his classical " Report on the Geology of Cornwall, 

 Devon, and West Somerset," though by no means dogmatic, are 

 strongly in favour of their entire independence of each other. 



The following is the concluding passage of his chapter on the 

 Mica Slate, Hornblende Slate, and Associated Rocks : — " Although 

 there may be some obscurity as to the mode in which the red and 

 grey argillaceous slates on the north come into contact with the 

 mica and chloritic slates, the line which separates them from each 

 other may be considered as well marked. There appears no passage 

 from one into the other which would authorize the supposition that 

 both were merely portions of a larger mass, one having been 

 exposed to different conditions from the other, subsequently to their 

 original formation, by which its first mineral character became 

 changed. Neither does there appear any mode in which we could 

 consider the one portion to have been buried beneath detrital 

 accumulations and then changed, according to the hypothesis above 

 noticed, without the adjoining mass having been subject to like 

 conditions. If the one be an altered portion of a larger mass, of 

 which the other constituted a part, it could scarcely have been 

 by this process. In the absence of any contradictory evidence, it 

 would appear fair to infer that these rocks [the mica slate, horn- 

 blende slate, etc.] belong to that class which is more ancient than 

 the grauwacke series ; and though the mica and chloritic slates of 

 the district may be associated with rocks possessing an arenaceous 

 aspect, even supposing they may be detrital, that they form no 

 part of that series which adjoins them on the north." Moreover, 

 it is important to observe that, in the explanatory column of his 

 Index-map, the colour by which the Metamorphic series is indicated 

 bears the legend " Chlorite Slate and Rock, Mica Slate and Gneiss." 



So far, therefore, as the publications of De la Beche himself are 

 concerned, there is nothing whatever to indicate that he favoured 

 the hypothesis of metamorphosed Devonians, which, as we have 

 seen, he regarded as by no means a likely solution of the problem. 

 Yet we are confronted with this difficulty, viz., that on the old 

 Geological Survey map the boundary between the two series is 

 indicated, for the most part, by a faint, dotted line, and the rocks 



