PRE-CAMBRIAN ROCKS OF ST. DAVID'S. 267 



into the fullest details. In the discussion of the subject I am mainly 

 desirous to get at the truth ; and I feel confident that my natural 

 and, I hope, laudable pride in the work done by my predecessors 

 and colleagues on the Geological Survey will not lead me for a 

 moment to forget the signal services rendered to the history of the 

 Cambrian rocks by Dr. Hicks, which no one can more cordially 

 recognize than I do. 



At the outset I may allude to a characteristic feature in the 

 literature of the subject. From the brief summary above given of 

 the various papers which have appeared, it will be clear that the 

 views at present entertained regarding the Pre-Cambrian age and 

 metamorphic character of the rocks of St. David's are the result of 

 a process of development during a course of years. Dr. Hicks at 

 first put forward the idea of Pre-Cambrianism somewhat vaguely 

 and timidly ; but each successive communication from him has shown 

 increasing boldness in the enunciation and extension of his doctrine. 

 Though interesting in itself, this evolution of opinion has been at- 

 tended with the disadvantage that so many of the statements and 

 views expressed in the earlier papers have since been tacitly modi- 

 fied or abandoned in the later ones, that it is difficult to know how 

 far these earlier publications are available for citation as expressing 

 Dr. Hicks's ultimate opinions. Indeed they appear to possess little 

 more than an historical value, as records of the successive stages 

 through which their author's present convictions have been reached. 

 I shall only cite them where their observations are not positively 

 contradicted in his later memoirs. 



It will be most convenient to discuss seriatim each of the three 

 alleged Pre-Cambrian groups at St. David's, beginning with the 

 oldest. This, moreover, is nearly the order in which my investi- 

 gations in the field were conducted. 



1. "Dimetian." 



Immediately to the south of St. David's a gentle ridge, roughened 

 here and there with rocky prominences, stretches in a south-west- 

 erly direction for rather less than two miles. Its component rock 

 is seen in scattered knobs, but in no continuous section, until, at 

 its seaward termination, from the bay of Porth-lisky eastwards for 

 about half a mile, it forms a rocky shore. This coast-section is the 

 only continuous exposure of the rock in the district. But laving 

 that rock bare as it does, both in horizontal ledges and vertical cliffs, 

 and revealing its contact with the adjacent strata, this coast-section 

 affords the geologist every facility for determining the structure 

 and stratigraphical relations of the rock that forms the ridge. 



In the original work of De la Beche, and in the subsequent investi- 

 gations of the Geological Survey, the rock in question was regarded 

 as eruptive, and as later in date than the Cambrian strata, through 

 which it was believed to have been intruded. At the time when 

 these observations were made, the study of petrography was in a 

 sadly neglected state in this country. We must not, therefore, ex- 



