340 . E. M. KINDLE 



It is^the purpose of the present paper to point out some of the 

 factors which make for periodic variabiht}- in the rate of deposition 

 and to cite some examples from existing lakes and seas to illustrate 

 the sharp contrasts in the rate at which sediments accumulate at 

 different points near the same coast hne. 



Some familiarit}- with the mobihty of wind-formed deposits is 

 unavoidable, but with the far greater mobility of water-laid 

 deposits we ha^•e a comparatively shght acquaintance. We are 

 apt to tliink of cla&tic deposits which ha^-e once come to rest on 

 sea or lake bottom as permanently tixed. That such materials 

 lose nearh' half their weight in water and in a corresponding degree 

 .their tendency to "stay put" is apt to be forgotten in considering 

 the liistor}- of geological formations. Removal or migration of 

 parts or the whole of an unconsolidated formation may occur much 

 more rapidly below than above sea level. The buoyancy of water, 

 together with the general absence of the tbdng influence of vege- 

 tation, gives to unconsohdated aqueous deposits under the combined 

 influence of waves and currents a far greater degree of mobility 

 and instability than subaerial deposits possess. 



CLASTIC DEPOSITS 



Observations on the Great Lakes. — PreAdous to human inter- 

 ference sand dunes represent in a moist cHmate an established 

 equilibrium between the forces of the winds and the waves and the 

 stabihzing influence of vegetation. The shght est interference by 

 man witli the vegetable covermg of a sand lull countr}- which is 

 usually fomid in temperate climates may. however, start the dunes 

 of a whole region traveling. It is said that the highest dmie 

 of Friesland owes its origin to the destruction of a single oak. 

 Water-laid deposits represent a similar balance of forces in which 

 water currents replace air currents. 



The deposits of the foreshore represent the iiuiermost zone of 

 sedimentation. They may be examined in part at least from the 

 vantage ground of the shore. Because of their comparative acces- 

 sibility to observation the deposits of bars, tickles, and spits illus- 

 trate well the irregular and highly locahzed character of the inshore 

 deposits. 



