408 THE THREE CLASSES OF DEPOSITES 



1. Modern depositions from the briny ocean. These* 

 as they consist of wearing away some places and adding 

 to others, are in daily operation. There can be no 

 doubt that such changes have always been going on 

 since our planet received its present configuration. 

 Many of them are subsequent to the commencement of 

 animal and vegetable life. 



2. Depositions from fresh water are also constantly 

 making. The showers of rain, the currents of rivers, 

 the trickling of springs, and the bursting of lakes, are 

 all instrumental in producing alterations of this kind. 

 From the nature of these productions they are deeply 

 connected with beings that have enjoyed life, as we 

 know from the vast number and variety of their fossil 

 remains. I consider these formations as subsequent to 

 the preceding in their origin and commencement, but 

 coetaneous ever since. 



3. Proceeding further back, the inland seas of salt 

 water present themselves. In North America they have 

 lost their briny quality, and become fresh lakes ; while, 

 in Asia, there are numerous instances of inland salt 

 seas to this day. The subsidence of the North Ame- 

 rican lakes in the first instance, and their conversion 

 from saltness to freshness in the second, are occurrences 

 of the most interesting nature. They have given a pe- 

 culiarity and distinctness of character to our geology, 

 which naturalists among us will learn to appreciate. 



4. After exploring the extensive formations of this 

 kind in North America, we are carried to the most an- 

 cient foundation, beyond which our inquiries are inca- 

 pable of penetrating. These materials probably consti- 

 tute the solid body or nucleus of the globe, according 



