A CONTRIBUTION TO THE GEOLOGICAL HISTORY OF 

 THE NORTH ATLANTIC REGION ^ 



By Prof. Albert Gilligan, D. Sc, F. G. S., M. I. Min. E. 



I. INTRODUCTION 



There may be said to be two main branches of geological investi- 

 gations — the physical and the biological — not, of course, that these 

 can be regarded as independent or divorced from each other, but to a 

 certain point they can make their contributions independently. For 

 a full history, the physical and the biological changes must be known 

 and their mutual relationship understood. It seems possible, how- 

 ever, that the physical history of the earth is likely to be known in 

 much greater detail than that of the fauna and flora, for the " dry 

 lands," tenanted as they undoubtedly were by various forms of life, 

 have left behind a record which can be fairly well traced on the 

 physical side but will always refuse to yield up all its secrets on the 

 biological side, since only rarely have the land animals and plants 

 been preserved by a lucky chance in the rocks accumulating at the 

 time of their existence. 



The permanence of continents and ocean basins has long been a 

 subject of controversy. Lyell, in his Principles of Geology, makes 

 reference to the early ideas of the Mediterranean peoples on this 

 subject, while L3^ell himself was of opinion that continents and ocean 

 basins do change places in tlie course of ages. 



This idea was earl}'- challenged by both physicists and biologists. 

 The physicists, led by Lord Kelvin, regarded the general framework 

 of the earth as having been fixed in very early times, and Kelvin 

 considered that the oceans and continents may have been mapped out 

 in the original nebula from which the earth had condensed. 



R. T. Chamberlin, in his book on the origin of the earth, favors 

 a very early delineation of the present distribution of land and 

 water, since he ascribes it to a time when the earth was still receiving 

 planetesimal material in quantity and " growing up." The bases of 

 his arguments are the effects produced by atmospheric circula- 

 tions, which in the embryonic earth had the same position and im- 



1 Presidential address delivered Nov. 23, 1929. Reprinted by permission from the Pro- 

 ceedings of the Yorkshire Geological Society, vol. 21, pt. 4, January, 1931. 



207 



