ANNlVEKSAlli ADDRESS OF TliE I'lCESlDKKT. 67 



can usually, I think, bo tolerably certain that the general facios of 

 the rocks is that which distinguishes those properly termed Archaean. 

 But at present 1 should bo sorry to affirm that this facies belongs 

 entirely to the most ancient gneisses. Nor am I aware of any reason 

 why rocks un distinguishable in composition and structure from 

 Archa3an masses may not be found in much younger formations. 



Keeping, then, the term " Archa)an" as a general designation for 

 the oldest gneisses and their associated rocks, w^hich may be still 

 further discriminated in local types, such as the Lewisian of the 

 Hebrides, we may separate from these any well-defined groups of 

 sedimentary or metamorphic formations intermediate between the 

 fundamental gneisses and the Cambrian system, such as have long 

 been known in Canada and the United States. The tendency on 

 the other side of the Atlantic seems, at present, rather towards the 

 multiplication of these groups, as the details of the more ancient 

 chapters of geological history become more fully known. But we 

 should, I think, at least in the meantime, avoid the identification of 

 any such primitive formations in distant unconnected regions. We 

 may discover that in Europe, as in North America, several groups 

 of more or less altered sedimentary strata intervene between the 

 Cambrian slates and the Archaean gneisses, but we shall do wisely to 

 refrain from trying to find Huronian, Keweenan, Animikie, Keewatin, 

 Coutchiching, or Laurentian on this side of the Atlantic, until we 

 have discovered some reliable test by which to fix their stratigra- 

 phical identity. It will be better to propose provisional local names 

 for such well-marked groups of pre-Cambrian rocks as may be found 

 to intervene between the Archaean platform and the base of our 

 Palaeozoic formations. 



I. ARCH^AN. 



The most ancient rocks of Britain are those termed by Murchison 

 the " Fundamental Gneiss." They are most extensively developed 

 in the chain of the Outer Hebrides, whence they have been termed 

 '• Hebridean," or from the island of Lewis, " Lewisian." The only 

 districts in which they have yet been investigated in minute detail 

 are those where, along the western borders of Sutherland and Ross- 

 shire, they emerge from under younger formations, and where they 

 have been carefully mapped by the Geological Survey. Until the 

 Hebrides have been studied in the same detailed manner our know- 

 ledge of these rocks must be regarded as notably incomplete. But 

 the investigations of the Survey, so far as they have gone, have put 



