162 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 16, 



coast of North and South Wales* On this scheme the great Cam- 

 biian system (or the great Cambrian division, for which of these 

 terms be used is to me indifferent) is to have neither name nor 

 colour on our geological maps ; and all the groups above described 

 (down to the Lingula beds inclusive) are to come under the colour 

 of the lower group of the Silurian system ; though that group (in the 

 typical country of Siluria) represents only the fourth and highest 

 group of the great Cambrian series of deposits. Why are geogra- 

 phical terms to be retained when we deprive them of their geogra- 

 phical meaning ? A good geographical term in geology must refer 

 us to a country which contains a good type of the series of rocks 

 designated by such term. This I consider a perfect axiom in nomen- 

 clature. The country described in the Silurian system does not 

 answer this essential condition. The term Lower Silurian, as ap- 

 plied to the older groups of the Cambrian series, cannot therefore 

 be retained with any propriety of language. 



The " Silurian System " was first offered to us as a definite upper 

 division of our great series of slate rocks, and it was separated into 

 definite groups, both the system and the several groups having geo- 

 graphical and local names. One value of the new names was this, 

 that they referred to an actual development in nature, and to good 

 local types, whether taken collectively or separately. But a far 

 higher value was implied in the fact, that the Silurian groups com- 

 pletely filled up the chasm between the older British slate rocks and 

 the Old red sandstone. Another great advantage in the publica- 

 tion of the Silurian system was the following : it enabled us to 

 break up into groups or systems the vast series of slate rocks which 

 had hitherto been defined by the names " fossiliferous greywacke," 

 or some other equally indefinite term. So far as it goes, the Silu- 

 lurian system offers us incomparably the best (and in some cases the 

 only) type of the upper division of the British slate rocks ; and as 

 it not merely offers us the best physical and zoological type, but, in 

 description, has the priority in time, the name " Silurian System " 

 can never, during the progress of discovery, disappear from a sy- 

 stematic enumeration of British formations. But of the whole pro- 

 tozoic, or older slate series, the Silurian system offers us no type 

 whatsoever ; inasmuch as the older Cambrian groups are wanting in 

 that system, as published by its author. To describe these groups, 

 in the technical language of the Silurian system, would therefore be 

 nothing more or less than this — viz. to describe a series of old rocks 

 of enormous thickness, and with well-defined characters, by words 

 which only acquire their meaning by reference to groups of strata 

 of a later period — strata which had no existence at the time these 

 older rocks were deposited : and assuredly to name an old group 

 of rocks by technical terms drawn from a newer group is a pro- 

 cess of nomenclature as incongruous as ever was attempted. Yet 

 such (so far as I comprehend it) is the process by which all the 

 old Cambrian rocks are to be included in the lower division of the 

 Silurian system. This extension of the Silurian system makes it 



