308 Dr Fleming on the Expediency of forming Harbours 



bourhoocl of the ancient and celebrated Dunottar Castle, 

 Eoveral small bays may be observed, deriving their origin 

 fi'om the beds of soft grey sandstone which alternate with the 

 conglomerate, and the latter being less destructible by the 

 action of the sea, forms the bounding nesses, aided in a few 

 places by amygdaloid or porphyry. In general, indeed, it will 

 be found that the observer of nature can seldom traverse any 

 considerable portion of the coast without, here and there, 

 meeting with sandy beaches, at the margin of bays, where all 

 traces of the rock have disappeared, and he may consider 

 himself fortunate if he succeed in detecting the solid materials 

 he is searching after, at low water-mark, or in some inland 

 ravine. 



The valleys necessarily form the recipients of the rain water, 

 and constitute river basins ; and the rivers thus formed by 

 them, and flowing through them, serve, in turn, to augment 

 their capacity, by carrying to a lower level the disintegrated 

 materials which have been produced by atmospheric influence. 

 These materials become accumulated at the junction of the 

 river with the sea, and constitute, in certain cases, those deltas 

 which frequently occasion a subdivision of the main stream. 



The disintegrated materials of the bay, associated in some 

 places w^ith those of the valley, and which usually consist of sand 

 and gravel, are era[)loyed in forming the sea-beach. The irregu- 

 lar but almost constant action of the ripple or wind-waves, 

 produces a uniform distribution of these materials, and as cer- 

 tainly restores the breach which disturbing causes may have 

 produced in its continuity. 



These materials, thus exposed to a ripple action variable in 

 its intensity and direction, are usually arrested in their pro- 

 gress by the nesses which limit the bays, so that the character 

 of the beaches of two contiguous bays may differ considerably 

 from each other. The beach of Aberdeen bay, e. ff., is sandy, 

 while that of the neighbouring bay of Nigg consists of very 

 coarse gravel. 



When a river, on its way to the sea, reaches a bay with its 

 margin constituted as we have been describing, it has to 

 maintain a constant warfare with this tendency to continuity 

 of the sand and pebbles of the beach. If, during a flood, the 



