PRESIDENTIAL ADDRESS. 405 



even persisted since the surface became suitable for the amatory escapades and 

 internecine enterprises of living organisms. 



Few geologists, for instance, will now urge with Hutton that a ' due propor- 

 tion ' has always been preserved between land and water on the surface of the 

 globe, if by those words is meant a proportion such as we now enjoy. We may 

 remark, in passing, that the proportion regarded with complacency by Hutton 

 may have suited the populations and ambitions of the eighteenth century ; but 

 recent events have at any rate shown the need for an expansion of the 

 continents. 



If we go back to early times, we must consider, -with E. A. Daly,' the 

 possible grouping of the land against which the Huronian or late pre-Cambrian 

 sediments were formed. The stimulating imagination of this author has pro- 

 posed a threefold explanation of the absence of calcareous coverings or 

 strengthenings from the organisms of primaeval seas. I use the word ' imagina- 

 tion ' advisedly, since the power of conceiving what has happened in the past 

 is not necessarily limited by observation of what is now going on around us. 

 The conclusions of Hutton as to the nature of the contact of granite and sedi- 

 ments in Glen Tilt, and those of G. P. Scrope as to the dynamic origm, or at 

 any rate the dynamic intensification, of foliation in crystalline rocks, are 

 triumphs of the imaginative faculty. The geologist who represses his imagina- 

 tion does, perhaps, excellent observational work ; but if this repression becomes 

 habitual, others will reap the intellectual harvest of which he has counted out 

 the seeds. 



R. A. Daly, then, has imagined, as one of the causes contributing to a 

 ' limeless ocean,' a primitive distribution of land and water very different from 

 that which determines our continental land to-day. His pre-Huronian land- 

 surface is pictured as merely a number of large islands, on which no long and 

 conspicuous rivers could arise. Granitic rocks, moreover, prevailed, and basic 

 materials, capable of supplying calcium in abundance, had not yet become 

 prominent in the surface-layers of the crust. 



It may be said that this primitive condition of the distribution of land and 

 Avater is very unlikely to return. But we have evidence that Hutton's ' due 

 proportion ' has been interfered with from time to time. The conversion of the 

 Danish area into islands in the human epoch, and the severance of the British 

 region from continental Europe, are merely pictures in little of what may 

 happen in an unstable crust. The very general spread of the sea over the land- 

 margins in Cenomanian times is attributable to a shallowing of the ocean- 

 floors, and it is difficult to say whether this process has been rhythmic or excep- 

 tional in the history of the globe. The Carboniferous period opened with 

 marine conditions over a large part of the northern hemisphere, indicating, not 

 only a continuation of the Devonian seas, but an overflowing of much of the 

 Caledonian land. The same period closes with an extension of the continental 

 edges, and the formation of swampy flats, in which the vegetation of the epoch 

 has been abundantly preserved. Similarly, the sea which deposited the 

 Cretaceous strata, after encroaching alike on South Africa and Scandinavia, 

 withdrew to a considerable extent in Eocene times, and its perpetuation along 

 the Mediterranean belt only calls attention to its subdivision or absence in other 

 areas. 



The Foundations of the Earth's Crust. 



Hutton, however, remains at present unassailable in one of his most remark- 

 able propositions. He was not troubled by any theory of nebular origins, nor 

 by isogeotherms and their gradual retreat from the surface on which we live. 

 For him, the oldest rocks that we know are sedimentary, and these sediments 

 differed in no respect from those of modern days. This conclusion has perhaps 

 not received the full attention that it deserves. It was based on philosophic 

 reasoning rather than on observation, and its world-wide truth has only recently 

 become appreciated. It now appears certain that we possess no record of a 



' 'The Limeless Ocean of Pre-Cambrian Time,' Amer. Journ. Sci., vol. xxiii. 

 (1907), p. 113; and more fully in 'First Calcareous Fossils,' Bull. Geol. Sac. 

 America, vol. xx. (1909), p. 157. 



