Serpentine Area and liliyoldes. 265 



not of much use. Thin sections failed to show what was the 

 nature of the orijrinal rooks from which they were derived. 



(7) The Succession of the Rocks. 



Thia cannot be said to be established yet, but considerable 

 evidence has been collected since Mr. Dunn's hurried visit. This 

 observer admitted that his ideas were only tentative. Two fea- 

 tures largely influenced Mr. Dunn's reasoning : — 



(1) The consideration of the limestone as Upper Silurian on 



Mr. Chapman's identification of the I'hUyst.rophia. The 

 trilobite had not then been found. 



(2) The interpretation of the black fragments in the conglo- 



merate as black sla.te, and probably, therelore, indi- 

 cating a post-Ordovician deposit. 

 An older age for the limestone now seems more reasonable, 

 and the argument of the black fragments does not hold, since 

 they are not slate, but fragments of a black igneous rock, as 

 shown by thin sections. Mr. Dunn regarded the Ordovician as 

 the oldest rock, the serpentine, or rather the original pyroxene 

 rocks, as intrusive into the Ordovician slates, while the frag- 

 mental serpentinous rocks and limestones were grouped as Upper 

 Silurian. The succession, however, which appears more correct 

 to the writer, would place the massive serpentine and allied 

 rocks as the oldest series — at least pre-Upper Ordovician ; next, 

 perhaps, the fragmental serpentine conglomerates, etc., lime- 

 stones and slates. Further fossil evidence is necessarj^ to deter- 

 mine whether further sub-division is necessary, but at present 

 the course most in conformity with stratigraphical evidence is to 

 consider the whole of the post-massive-serpeutine series as 

 Upper Ordovician. 



\.— The Rhyolites and Associated Rocks of the Upper 



Palaeozoic Series. 



As the writer has no time at present to do justice to the in- 

 formation collected on these rocks, they will be included simply 

 to render available some analyses which were made last year 

 in the University laboratory. The lavas include both acid and 



