W. H. Hudlesfon — E. Margin of N. Atlantic Badn. 103 



a fragment of the supposed ancient continents, nor of the deposits 

 which must have resulted from their denudation. 



Unless this reasoning has been upset by fresh evidence, it ought 

 to have considerable weight with geologists. No doubt some of the 

 West India islands, and notably Barbados, afford examples of oceanic 

 deposits of Tertiary age resting upon terrigenous deposits known as 

 the Scotland Beds. Nevertheless, even Barbados lies inside the true 

 suboceanic continental slope which margins that side of the Atlantic, 

 whilst the Caribbean Sea may be regarded as a region of exceptional 

 oscillation, which partakes to some extent both of an oceanic and 

 a continental nature. The Mediterranean in a less degree presents 

 similar features, and it seems to me that no valid argument can be 

 based on events which have occurred or are occurring in such 

 abnormal areas. 



Another very specious argument against permanence is derived 

 from the great height to which marine Tertiary beds, such as the 

 Nummulitic, are raised in the Alps, Himalayas, etc. Why may not 

 changes of equal magnitude, it is urged, have taken place conversely 

 in areas now occupied by the great oceans ? It should be borne in 

 mind, however, that the upheaval of Tertiary marine beds to these 

 great heights naturally takes place in mountain ranges, where 

 tangential pressure is at a maximum along lines which are of great 

 length but very limited in width. Such features can hardly be 

 compared with the great ocean expanses, whose breadth is measured 

 by thousands of miles. On the other hand, there is a considerable 

 degree of analogy between these prolonged mountain ranges and 

 the suboceanic continental slopes which bound the great oceans. 

 Both classes of phenomena are largely due to tangential pressure, 

 the result of secular contraction. Hence for the most part 

 mountain ranges are believed to occur and reoccur with nearly 

 the same orientation throughout geological time. They form the 

 lines of adjustment, as it were, in the earth's crust, which became 

 especially acted upon at certain epochs ; and the fact of marine 

 Tertiary strata having been raised to heights ranging up to 20,000 feet, 

 although it shows oscillation to a great extent within a long and 

 narrow area, does not justify the idea of an equal amount of oscilla- 

 tion in the ocean basins. 



The principal region of vertical movement in connection with the 

 oceans is probably to be sought in the suboceanic continental slope, 

 and such movements would affect the shelf or continental platform 

 more than the abyssal floor, which would remain comparatively 

 unaffected. In this way the upper portions of the submarine slopes 

 on the sides of the Atlantic may have emerged at times along the 

 line, more in some places and less in others, thus constituting 

 saliences which were worn back by the planing action of the sea ; 

 and in this way the Continental shelf, or rather portions of it, may 

 be of considerable antiquity. 



If this view be correct it will allow for a considerable amount of 

 change throughout geological time on the margins of the great 

 oceans without materially affecting the ocean basins themselves. 



