144 N. S. SHALER — EVIDENCES AS TO CHANGE OF SEALEVEL. 



more complicated than it is generally assumed to be. We are, however, 

 as will shortly appear, but at the beginning of the entanglement of actions 

 which affect the plane of the sea in relation to that of the land. 



SUBMARINE FOLDS. 



Strabo noticed the probability that changes in the level of the ocean- 

 floor were likely to affect the incursions or excursions of the seas. Our 

 better knowledge enables us to note the fact that the topography of the 

 sea-bottom leads us to discern something as to the movements which 

 bring about vast displacements of water. The recent advances in the 

 inquiries concerning the form of the lithosphere beneath the oceans 

 show us pretty clearly that the larger part of that area is occupied by 

 broad, rather gently sloped ridges which in a general way, except for the 

 absence of mountainous relief, resemble the continental upfolds. I have 

 elsewhere * suggested that these folds of the deep are in effect unemerged 

 continental masses; that a continent is one or more of these folds, gen- 

 erally a plexus of them, which has attained the realm of the air and in 

 that realm has been subjected to the erosions and consequent dislocations 

 which give rise to the characteristic topography of the great land areas. 

 For the present we are concerned with another influence which arises 

 from these submarine foldings, namely, the general changes of ocean- 

 level which are brought about by their formation. The variable depths 

 at which these undulations of the deep sea-floors lie, as well as what we 

 know concerning the bathometric conditions of formation of the stratified 

 rocks, make it reasonable to suppose that these unemerged folds are 

 subject to swayings and in general to an upward growth, such as has 

 presumably brought certain of them to the state of the continents. In 

 the paper above referred to I have noted the fact that certain topographic 

 features, such as the peninsula of Florida, appear to be folds of the nature 

 referred to, which in the process of their elevation have recently been 

 raised above the sealevel. 



Although it is eminently probable that the elevation of the submarine 

 folds is attended by a greater or less downward motion of the troughs 

 which lie between them, it is not at all probable that in the movement 

 the conservation of areas is anything like perfect. It is more likely, in- 

 deed, that at one time in the earth's history the effect has been to lift the 

 general sealevel in relation to the continental masses and at another to 

 lower it. When, in the process of upward growth, the submarine conti- 

 nent comes to be in part subaerial the further swayings of the mass will 

 be yet more effective in changing the level of the ocean. Thus, if North 

 America should remain undisturbed while the Eurasian mass underwent 



* Bull. Geol. Soc. Am., vol. 5, December, 1893, p. 203. 



