THE OLDER ROCKS AT ST. DAVIDS. Ill 



two distinct series, Dlmetian or lower, and Pebidian or upper series. 

 The chief point of this distinction lies, I think, in the admirable 

 way in which has been shown by careful survey and as careful 

 reasoning, that these are in fact two separate series, unconformable 

 to each other, as they are both to the Cambrian which overlaps 

 them indifferently. These points seem to have escaped previous 

 observers ; indeed they seem to require such intimate knowledge of 

 the ground for their appreciation, that they have not been 

 unreservedly accepted. The matter is so comparatively new that 

 there seems still room for further research and discussion. 



The few remarks which I have to make are founded on the 

 examination of the crystalline rocks which were collected carefully 

 in place, with a view to subsequent examination by the microscope. 

 I should state at the outset that I provisionally accspt Dr. Hicks' 

 conclusions, though the microscope examination leads me to look 

 upon some of the rocks rather differently, — too minute a criticism 

 it may be said if it does not alter the outcome of his contentions. 



JDimetiayi. The rocks which compose this series are said to be 

 *' chiefly compact quartz schists, chloritic schists, and indurated 

 shales,'' [loc. cit. p. 231]. They are all considered to belong to a 

 metamorphic series. Dr. Hicks notices their change in character 

 from N. of St. Davids, where they are said to be more highly 

 crystalline, towards the S. where they are less highly meta- 

 morphosed. At Forth Lisky they are termed quartz-schists. 

 There is thus a change along a N.E. — S.W. direction — according 

 to our author the direction of dip of the old series, — which by 

 metamorphic action have become the now highly altered Dimetian. 

 This change, along a determinate direction (dip), and constancy of 

 character along the strike, is a most important point, and fully 

 proves, I fancy, if we accept the facts, that the so called Syenite of 

 former authors is not an irruptive rock, but truly metamorphic. 

 The discovery of the metamorphic nature of the lower Pre- 

 Cambrian series seems to me a most interesting point. The 

 history of the existing sedimentary series, of which we see now 



