Dr. H. Hicks — On Rock Classification. 



359 



The subordinate divisions should as far as possible have Geographical 

 terms with wide applications, but such names as Carboniferous and 

 Cretaceous will also doubtless remain in use. 



The wide geographical divisions should be divided and subdivided 

 under more local names. The Lower Palaeozoic rocks in the West 

 of England and Wales could according to this plan be satisfactorily 

 arranged as follows : — 



I would apply the term Cambrian in a far more general sense than 

 it has hitherto been used, and would place it as one of the main divi- 

 sions of the Palaeozoic, the others being Devonian and Carboniferous.^ 



Cambrian, being a term derived from the whole of the Principality 

 of Wales, where the Lower Palaeozoic rocks are best exposed, and 

 in which every important group from the base of the Llanberis and 

 Harlech series to the top of the Ludlow is found, is incomparably 

 the best that can be suggested for this purpose.^ 



The Cambrian in this arrangement should be broken up into three 

 primary divisions with the names in descending order of Silurian, 

 Ordovician, and a new name Georgian, from the districts bordei'ing 

 St. George's Channel, where the lower rocks (Llanberis, Harlech, 

 Menevian, etc.) are best exposed, and where they have been mainly 

 examined. The groups and series should have local names — such 

 names being taken from places where the beds were first examined, 

 or are well exposed. 



The following table will explain the arrangement suggested : — 



Systems. 



Primary Divisions. 



Groups or Stages. 

 ("Wales, etc.) (Scotland) (Ireland). 



CAMBRIAN. <^ 



Silurian. 



Ordovician. 



Georgian. <^ 



Ludlow 



p 



Wenlock 



? 



Llandovery 

 Bala 



? 



Llandeilo 



P 



Llanvirn 



? 



Arenig 

 Tremadoc 



? 

 ? 



Dolgelly 

 Ffestiniog 



p 

 P 



Maentwrog 



p 



Menevia (instead 

 of Menevian) 

 Solva 



? 



? 



Caert'ai 



? 



ABCH^AN, or, pre- CAMBRIAN. 



1 It may be found advisable to class tbe Upper Palseozoic Rocks, like the Lower, 

 into one system with three Primary divisions. In that case the term Devonian 

 would be applied, in a better sense, as the lowest of the Primary Divisious in that 

 system. 



2 The term Silurian may possibly occur to some as suitable, but to my mind it 

 seems entirely out of the question, as comparatively only a few of the groups,— none 

 indeed of the more important of the lower groups, — occur anywhere within the 

 limited area formerly occupied by the Silures. 



