IKTRODUCTIOE". 



Lakes have their birth ami death in the topograpliic development of 

 the land. A certain class form a characteristic feature of lands recently 

 elevated above the sea; others belong with the earlier stages or youth of 

 streams ; while still others appear during maturity or in the old age 

 of the rivers to which they owe their origin. Lakes of a different type 

 are associated with modifications of topography due to glacial and to 

 volcanic agencies, and to movements of elevation and depression in the 

 earth's crust. 



Lakes, like mountains and rivers, have life histories which exhibit 

 varying stages from youth through maturity to old age. The span of 

 their existence varies as do the lives of animals and plants. Li arid 

 regions they are frequently born of a single shower and disappear as 

 quickly when the skies are again bright ; their brief existence may be 

 said to resemble the lives of the Ephemera. Again, the conditions are 

 such that lakes perhaps hundreds of square miles in area, are formed each 

 winter and evaporate to dryness during the succeeding summer ; these 

 may be compared with the annual plants, so regular are their periods. 

 Still othei-s exist for a term of years and only disappear during seasons of 

 exceptional aridity; but the greater numl)er of inland water bodies 

 resemble the Sequoia, and endure for centuries with but little apparent 

 change. So long are the lives of many individuals that liuniau history 

 lias recorded only slight changes in their outlines, but to the geologist 

 even these are seen to be of recent origin and the day of their extinction 

 not remote. 



The tracing of the life histories of lakes and the recognition of the 

 niinicrous agencies that vary their lives and lead to their death, gives to 

 this bi'unch of physiography one of its |)iiii('i]ial charms. 



