SAND-SPIT HARBORS 199 



Ordinaril)' the projections arc straight, but where in the course 

 of their c^rowth their extremities come in contact with strono- 

 currents, they may ho. turned so as to make hooks of remark- 

 ably curved or anguhir outHne, occasionally enclosing consid- 

 erable sheets of water of sufficient depth to have value for 

 harborage purposes. Provincetown Harbor, on Cape Cod, is 

 an example of this nature. That at Cape Pogue, on Martha's 

 Vineyard, though the embayed waters are very shallow and 

 have no value for jnirposes of shelter, is, as an illustration of 

 \the process b)- which these hooks are formed, one of the most 

 interesting structures belonging in the group. 



The directions in which sands journey along the shore, as 

 well as the speed of their movement, depends mainly on the 

 attitude of the coast-line in relation to the prevailing winds 

 and currents. These effects may be traced, not only in a 

 local way, but sometimes throughout a far-reaching extent of 

 shores. Thus on the Atlantic coast from Chesapeake Bay to 

 Cape F"lorida, the prevailing course of the sand is to the 

 southward. The beaclies have been characterized by a move- 

 ment in that direction since they first came to be observed. 

 To this endless procession of sands is due the southward 

 march of the ever-changing inlets in the manner indicated 

 in the description of lagoon harbors. This movement of 

 sands toward the south along the Atlantic shore is due, in 

 part at least, to the fact that while that coast-line extends 

 in a general northeast and southwest direction, the prevailing 

 winds and tlie waves which they produce are from tlie points 

 between east and north, so that the surges strike the coast at 

 an oblique angle and tend to urge the detritus toward the 

 southern part of Florida. At the cape of that name we find 

 the southern extremitv at which these marching sands have as 



