OF SAND FORMATIONS ON MARINE COASTS. 23 



of the waves combined with the drifting of the winds. But the sloping 

 part swept by the waves below high-tide level is very evenly stratified 

 parallel to the surface: This surface dips usually at an angle of 5° to 

 15°. Generally speaking the coarsest beaches have the steepest slopes. 

 The sand of the beach is increased or decreased according to the weather — 

 and the seasons, it being thickest in summer and thinnest in winter, and 

 sometimes the beach is almost stripped of sand after a series of gales. 

 On the beach, there is formed a ridge of sand during offshore winds. 

 The sand is readily raised by the breakers and usually an excavation 

 or trough is found at the back of the ridge. This is similar to the 

 excavation and elevation produced in ripples. When the wind goes 

 down, a succession of low ridges are formed concave on the side toward 

 the sea, but as soon as a wave reaches over the top of the ridge, the 

 concavity is filled and an edge with uniformly sloping sides is formed. 

 The height of this beach ridge is usually not very considerable on the 

 Baltic coasts; seldom more than 1.5 m. over the general level of the 

 beach, or 2.25 over the sea. On the Atlantic and Pacific coasts, the 

 height is not much greater, although the ridge is formed by breakers 

 of considerable strength. 



When the breaker line has been stationary for some time, for 

 instance during a high tide, an excavation is dredged out, and at ebb a 

 lagoon is often left here. For our purposes the beach may be divided 

 into the following belts : 1. The submerged beach; 2. The front beach; 

 3. The middle beach; and 4. The upper beach. The first belt includes 

 that portion of the beach that lies below mean low tide, but which may 

 be exposed by neap tides. It is normally covered with water, and is 

 subjected to the constant beating of the waves, which carry the material 

 ashore in their landward advance. Some of the detritus is deposited, 

 while another part is returned seawards with the undertow. Where the 

 carrying power of the surf is great, the beach is often built up by 

 material containing a considerable amount of coarse gravel and pebbles. 

 On such beaches there is always a residue of mud after a storm or an 

 exceptionally high tide, while no such deposits occur on sand alone. 

 The front beach is the belt between mean low tide and mean high tide, 

 being alternately each day exposed to the air and submerged. It mostly 

 passes without any marked break into the submerged belt. Situated on 

 the border between the land and water the front beach offers very 

 unfavorable conditions, not allowing the deposits to remain stable or 

 resting, on account of the repeated washing of the waves and currents. 



With the term middle beach we would designate that portion of the 



