deporminCt agekcies affecting shorelines. 147 



Rally an indented margin to a straight beaeli. If an emerged fold re- 

 mained with no change in elevation after it had attained the surface, 

 the normal result would he the gradual obliteration of the relief by the 

 inward march of the marine bench, ending with tlie formation of a 

 benchcd-otf shoal. It is evident that with a given elevation of the origi- 

 nal fold the character of the surface from the center of the land to the 

 center of the neighboring seas will depend upon an equation in which 

 there are four factors — the original height of the surface, the rate of down- 

 wearing on the land, the rate of inwearing of the sea, and the rate of ac- 

 cumulation of the detrital shelf off the coast. Thus in a newly emerged 

 fold the bench-work of the sea and the corresponding land scarf will be 

 small, as will also be the submarine shelf, which is the product of the 

 land waste and of the organic matter originating in the sea which is de- 

 posited upon that accumulation. It is evident also that each of these 

 groups of agents is subjected to innumerable slight variations. The 

 emerged folds will not be homogeneous in their constitution, the rate of 

 land-wearing will vary, according to the distribution of the rainfall and 

 the streams to which it gives rise, and the growth of organic material in 

 the sediments off the shore likewise varies at different points. We may, 

 however, for the present neglect these innumerable modifications of the 

 factors and note merely the conditions, in a somewhat ideal way, of our 

 supposititious newly emerged fold. We see that the geologic work done 

 upon it leads to a transfer of its rock matter by the streams and waves, 

 either into the state of solution or in the immediately detrital fonn, to 

 the sul)marine shelf. 



Oscillations. — Owing to the very numerous causes which lead to changes 

 in the elevation of shorelines, the simple condition of an emerged fold of 

 the lithosphere, which does not afterward change its position until it 

 attains the stages of a benched-off shoal, is practically unknown. All 

 areas the history of which I have been able to ascertain show the result 

 of numerous oscillations in the relative level of sea and land. ICven in 

 the case of Florida, as I shall afterward note more in detail, there are 

 reasons to believe that the fold has oscillated with reference to the sea 

 through a range of near a thousand feet since the time when it first 

 pushed the waters apart. In these vertical swa3ings it is easy to see that 

 the zones of action overlaji each other. In a process of elevation thecoast- 

 line, followed up ])y the zone of atmospheric erosion, will pass out on the 

 depositional shelf. In i)eriods of subsidence the coastline, fcdlowed by 

 the depositional shelf, will invade the zone on which the record of sub- 

 aerial actions is written, in fact, along any shore-belt, counting as such 

 the zone within which the coastline has swung, it becomes a matter of 

 first importance, though one of exceeding ditliculty, to determine the 



