IN THE DEGRADATION OF THE LITHOSPHERE. 399 



3. Atmospheric erosion and marine planation are two separate 

 phases of a general process of lithosphere degradation which are 

 frequently connected into consecutive stages by the presence of 

 joint lines which extend from beneath sea level up into the mass of 

 the lithosphere above sea level ; these lines are also horizontal and 

 thus act to produce flat surfaces. 



4. Degradation of the lithosphere surface may occur also by 

 the vertical displacement of these joint segments irrespective of 

 atmospheric or marine contact. 



5. Joint control of lithosphere degradation has been active since 

 the period when the lithosphere possessed a solidified structure and 

 has been a fundamental factor in the evolution of the lithosphere, 

 or geomorphology. 



Detailed Observations on Plates VI.-VIII. 



Plate VI., Figs, i and 2. These sands are entirely unconsolidated but 

 are rather gritty. Rehoboth Beach, Delaware. 



Plate VII., Fig. 3. Joint disintegration in quartz-mica-garnet schist, 

 Prouts Neck, Maine. The loose segments fall to water level and through a 

 pebble-gravel process are reduced to quartz and garnet sands, the mica washes 

 to sea. The original rock character is thus totally destroyed by a rapid me- 

 chanical action working through joints. 



Fig. 4. Bowlder flat at Sea Point, Maine, above Portsmouth Harbor. 

 Tliis flat is composed of incompletely reduced joint blocks from the adjacent 

 rock masses and appears to be built out over a reef which lies parallel to a 

 series of other reefs and small rock segments in place. The flat is a prolific 

 breeding and feeding ground for vast colonies of mollusca, small Crustacea, 

 lime secreting algae, Laminaria and other forms of animal and plant life. 

 Angular blocks coated with lime carbonate are frequent. The relation of such 

 bowlder flats to life distribution suggests interesting paleographic analogies. 



Plate VIII., Fig. 5. Block disintegration proceeding in a folded area in 

 coastal plain. The folds are now to be seen with their tops in most cases 

 cut ofif and are broken into blocked segments. This fracture may be seen 

 to extend below the level of the cHfif. Near Ogunquit, Maine. 



Fig. 6. Angular edges forming an abi'upt series of sea terraces. The 

 entrance of one of a series of parallel coves or small bays may be noted. In 

 front of the cliff extends a broad platform iliduced by the horizontal jointing. 

 Clififs near Ogunquit. Maine. 



(All of the illustrations are from photographs taken by the author.) 



