16 



GENESIS AND DEVELOPMENT 



As will be seen from this table, silica in all cases both in salt and 

 fresh water settled faster than clay. Whether this fact was merely a 

 result of a greater weight of the siliceous particles, or whether other 

 factors influenced the sedimentation, I was unable to decide. At all 

 events it was evident that the salt produces a considerable flocculation 

 in the water. The primary cause of the growth of the deposit in water 

 is sedimentation, but in many cases the rising of the level of the coast- 

 line has to be taken into consideration as a secondary factor. It is 

 often difficult to determine to what extent the rate of growth of a 

 deposit is due to one of these factors or the other. Especially is this 

 the case on a low coast, where the growth always takes place more rap- 

 idly than on a steeper shore. The horizontal growth of the deposit is 

 also much greater on coasts protected by islands than on open coasts 

 with deep water, where the material is more easily carried away. 



With regard to the position of the marine sediments it will be 

 noticed that they are apparently horizontal, and the tendency is to level 

 the beds through filling all depressions. The coarser sediments are 

 always nearer the shore in comparatively • narrow lines, parallel to the 

 coast, whereas the finer sediments are spread over a larger area further 

 off the shore. Banks and beaches are always sloping gently seawards, 

 and they are, perhaps, somewhat steeper on marine coasts than on fresh 

 water shores, general conditions being equal. 



