ANCIENT SHORE LINES AND EARTH MOVEMENTS IN 



MAINE 



By Edward H. Perkins 



One effect of geological study is to remove many of the 

 popular ideas in regard to our earth. One of the most 

 strongly held of these ideas is that the earth, outside of a 

 few earthquake regions, is firm and unchangeable. Geolo- 

 gists have shown us, however, that our terra firma is in more 

 or less constant movement, now rising, now sinking, as 

 compared to sea level. The object of this paper is to con- 

 sider some of the evidence on which the geologist bases 

 his theories of earth movement or diastrophism. It happens 

 that in our State we have many of the lines of evidence well 

 displayed. 



As we look at our sea coast today, the thing that im- 

 presses us is its extreme irregularity. Deep bays indent the 

 shore line and many islands rise to greater or less heights 

 above the sea. The deep bays gradually pass into larger riv- 

 er valleys, while on the seaward side soundings show the 

 continuation of the valley depression far out to sea. Most 

 of the islands appear to be continuations of the hills and 

 ridges of the main land. These features are well shown 

 in the new topographic map of the U. S. Geological Survey. 

 In these maps the configuration of the sea bottom is shown 

 by contour lines in the same manner as the land surfaces, 

 A study of these maps clearly shows that we have either 

 a rising of the sea or a sinking of the land. The valleys 

 are flooded by the ocean and the ridges are covered save for 

 the higher portions which now appear as islands. 



This shore line is a thing of today. For a record of the 

 past we must look for old shore lines and their character- 

 istic features. These old stands of the sea are indicated by 

 two lines of evidence; erosion or the distructive work of 

 water, and deposition or the constructive work. 



The erosive work of the sea is due to wave action and is 

 limited to a zone between the wave base beneath the surface 

 and the point on the coast reached by the highest storm 

 waves. Within this limited area the sea is tearing into the 

 land. Behind it leaves a gently sloping cliff or wave cut ter- 

 race marking the lower limit of wave action. Landward 

 the advancing notch undermines the shore until the rock 

 gives way and falls in fragments to the shelf below. These 

 boulders are seized by the waves as tools for its work and 

 hurled by the waves against the shore until they are ground 

 to sand and carried out to quiet water. If the land should 



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