232 SEA AND LAND 



weeds is traceable in the extensive deposits of angular debris 

 ruptured from the cliffs and distributed over the bottom in part 

 by the waves, but in a more considerable measure by the action 

 of ice. In the winter season the water freezing next the shore 

 entangles large quantities of the detrital matter formed in the 

 manner above described and when this shore ice drifts away 

 with the tide the rocky fragments' are likely to fall at some 

 distance from the marofin of the water. 



Where a harbor is of moderate depth over all of its area, 

 where the low tide comes against cliff shores and the bottom 

 is of a rocky nature, we ordinarily perceive little effect upon its 

 conditions arising from marine vegetation. Where, however, 

 the floor of the basin is to a large extent bare at low tide, and 

 especially where mud is formed in considerable quantities, we 

 can ordinarily notice the results arising from the growth of salt- 

 loving water plants. They are very evident to the eye and 

 may be traced on any well-made charts. As before remarked, 

 the most of this work is done, not by algae, but by the higher 

 flowering species, of which the greater part belong to the 

 families of grasses and sedges. The constructive work, how- 

 ever, which leads to the filling in of the harbor is, at least in 

 the regions north of Cape Hatteras, begun in the depths of the 

 water by the species known commonly as the eelgrass (yZostera 

 niaritima), a flowering plant which has the almost unique 

 characteristic of blossoming, fertilizing its flowers, and fruiting 

 beneath the level of the water. The conspicuous parts of the 

 plant consist of thin blade-like leaves, about a fifth of an inch in 

 diameter, but sometimes eitrht or ten feet lon^r. Owino- to their 

 strength these blades of the eelgrass withstand the impulse 

 of surges, such as act in the protected waters of harbors, 

 and by their thick- set order they diminish or entirely arrest 



