7o8 ROLLIN D. SALISBURY 



ity which resulted from the development of shore terraces in a lake 

 which stood much higher than the present lake after the ice melted. 

 2. If a coastal region affected by well-developed valleys is sub- 

 merged, the lower ends of the valleys become bays. Shore deposits 

 may be made across the mouths of the bays, converting them into 

 lagoons. The lagoons may then be silted up. If the region be sub- 

 sequently elevated relative to sea-level, the streams coming down 



Fig. I. — The slope of Lake Chelan, showing topographic unconformity. 



the mature valleys above cut new valleys across the new lands 

 recently emerged. The result is that valleys and topography of 

 greater or less maturity above are succeeded coast-ward by 

 valleys and topography which are much younger. Fig. 2, from 

 the coast of California, affords an illustration. 



It is, of course, clear that the same sequence of events may affect 

 a lakeshore, where it is clearly the level of the water which fluctuates. 

 Illustrations of topographic unconformity are perhaps more readily 

 drawn from lakeshores than from seacoasts, for notable changes 

 of water-level are here more common. The borders of Lake Chelan, 

 already referred to, furnish a good illustration, and the shores of 



