ANNIVERSARY ADDRESS OF THE PRESIDENT. 65 



I propose at present, therefore, to deal only with the earlier half of 

 the story, and to trust to your kind favour for another opportunity 

 of telling the remainder of my tale. 



It will be generally admitted that our knowledge of the rocks of 

 the earth's crust older than the Cambrian system is still exceedingly 

 vague and imperfect. We speak of them as " pre-Cambrian " or 

 " Archaean," as if they represented a definite section of geological 

 time, comparable to that denoted by one of the Pala30zoic systems. 

 Yet it is obvious that under these names we include a most multi- 

 farious series of rocks which represent not one but probably many 

 and widely separated periods of geological history. We cannot 

 suppose that the Cambrian fauna betokens the first beginnings of 

 organic being upon our planet. On the contrary, it must have 

 belonged to a time when invertebrate life had already reached such 

 a stage of advancement and differentiation that various leading 

 types had appeared which have descended, in some cases with 

 generic identity, down to our own day. There must have been a 

 long pedigree to the Annelids, Crustaceans, Brachiopods, Gasteropods, 

 and Cephalopods of the oldest known fossiliferous rocks. And some- 

 where on the earth's surface we may yet hope to find the stratified 

 deposits in which the remains of some of the progenitors of these 

 early tribes have been preserved. 



Unfortunately, the older layers of the terrestrial crust, where they 

 might have been looked for at the surface, have suffered sorely from 

 the mutations of the geological past. They seem in large measure 

 to have been either so efi'aced by denudation, or so altered by meta- 

 morphism, as to be no longer satisfactorily decipherable. But under- 

 neath the most ancient rocks, which, though now often crystalline, 

 may be regarded as of sedimentary origin, and wherein traces of 

 organic remains may still be looked for, lie coarse, massive gneisses 

 which preserve all over the world a singular sameness of structure 

 and composition. What might be found below these gneisses no 

 man can say. They are the oldest rocks of which we yet know 

 anything, and whatsoever may be our theory of their origin we 

 must, at least for the present, start from them as the fundamental 

 platform of the terrestrial crust. 



The present confused nomenclature of the oldest rocks is onh' a 

 faithful reflection of the vagueness of our knowledge of the geological 

 relations of these ancient formations. The term " pre-Cambrian " has 

 no doubt been, and may still be, a convenient designation for that un- 



