Vol. 50.] ANNIVERSARY ADDRESS OF THE PRESIDENT. IOI 



of a series of Banded Slates and Laminated Grits, with some inter- 

 calated bands of felsite or felsitic matter — this sequence being 

 unbroken until the great mass of felsite on the west side is reached. 

 He correlates the adit conglomerate with the Ehiw-wen Grit of his 

 previous paper, and the rest of the sedimentary beds with tbe 

 middle and lower series of his Caernarvonshire Cambrians, after 

 making due allowance for local changes. There are at least four 

 bands of felsite in various parts of the series, clearly not intrusive, 

 and usually associated with tuffs ; whilst most of the grits are 

 obviously composed of their debris. They are not at all meta- 

 morphosed, but only cleaved. He further describes the outcrops 

 as generally corresponding to the indications in the section, and 

 argues that the conglomerate and grit on the summit have no 

 connexion with the thin quartz-conglomerate in the adit. As these 

 have to be provided for, he suggests that they may possibly be an 

 extension of the Bronllwyd Grit and overlying rocks. 



It can hardly be supposed that the great Cambrian controversy 

 in North-west Caernarvonshire has been definitely settled by the 

 series of papers to which I have just drawn your attention. "We 

 perceive, it is true, that other gladiators have entered the arena, 

 and that the fight waxeth hotter even than before. But who can 

 tell what the end may be ; or rather, who shall attempt to estimate 

 the value of a name ? If we refer to page 83 of this Address, it 

 will be found that the green slates at the top of the Penrhyn quarry 

 contain that Conocoryphe viola which, we are told, must be included 

 in the lowest Cambrian. Thus we are at once brought to recognize 

 the fact that the lowest Cambrian of the palaeontologists forms the 

 summit of Prof. Blake's Cambrian. Hence there are two Cambrians, 

 a fossiliferous and an unfossiliferous series, which may indeed belong 

 to one system, though at present that must not be taken for granted. 

 Where there is any doubt we shall naturally be guided by palaeonto- 

 logy, since any other method of ascertaining the age of beds, except 

 where the stratigraphy is indisputable — and no one will say that of 

 North-west Caernarvonshire, — is liable to serious error. A point in 

 favour of Prof. Blake's view is that the Penrhyn slates seem to 

 constitute one series, so much so that nobody would ever think of 

 separating the Upper Green Slates from the Purple Slates and associated 

 grits. The unfossiliferous beds then may be regarded as possibly 

 Cambrian — down to what line shall we say ? Here comes the 

 difficulty. The middle and lower subdivisions of Blake's Cambrian, 

 so far as one can judge by description, do not seem very promising 



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