BOCKS OF THE ATLANTIC COAST OF CANADA, ETC. 817 



areas as contrasted with those of the continental plateaus. It also 

 indicates a persistence, on the whole, of the oceanic character of the 

 Atlantic depression. 



Lastly it shows the necessity in any system of geological classifi- 

 cation of distinguishing the continental plateaus, the lines of great 

 foldings and of igneous action, and the ancient ocean-margins from 

 each other, and of adapting our arrangements and nomenclature to 

 their actual diversity. In order to do this, while adopting common 

 designations for the great ages of geological time, and for those 

 systems of formations which mark the successive submergences and 

 emergences of the continental plateaus, separate classifications must 

 exist for the diii'erent kinds of areas, in tlieir details. It is also, I 

 think, necessary that we should not tie ourselves down to hard-and- 

 fast lines either as to the limits of systems or as to the relative values 

 of their divisions in widely separated localities, as these differ in 

 nature, and nothing is to be gained by conventional arrangements 

 overlooking these dilferences. 



Finally, I can imagine that many questions which have not 

 occurred to me may present themselves to the minds of other 

 geologists who may read or hear this paper. Should I possess any 

 facts tending to the solution of such questions, and not stated in 

 the above pages, they will be at the service of any one desirous to 

 use them for the advancement of science. 



Discussion. 



The President, whilst recognizing the importance of the paper, 

 doubted whether the question of correlation of the Pre-Cambrian 

 rocks on either side of the Atlantic was ripe for discussion. 



Dr. Hicks felt sure that the paper would be welcomed on this 

 side of the Atlantic. He agreed with most of the conclusions of 

 the Author, including the correlation of the Huronian with the 

 Pebidian. This was borne out, not only by similarity of lithologi- 

 cal characters, but by the exact correspondence of the succeeding 

 beds in the two areas as shown by Mr. G. P. Matthew. The diffi- 

 culty of correlation lay with the rocks below the Huronian. He 

 noticed that fragments of granitoid rocks occurred in the Huronian 

 as in the Pebidian. He also had called attention to the contrast be- 

 tween the Palaeozoic rocks of the ocean borders and those of the 

 interior of the continents, in papers read before the Society and else- 

 where. 



Dr. Scott referred to Mr. Walcott's work, and mentioned the 

 occurrence of great deposits of Pre-Cambrian rock in Arizona. 

 Where terrestrial species play an important part, difficulties of corre- 

 lation were much increased. 



Dr. HiNDE noticed the difference between the coast-geology of 

 America and that of the interior. 



Mr. Mark stated that the paper referred very fully to the point 

 noticed by the last speaker. 



