10 PRINCIPLES OF PALAEONTOLOGY. 



at the mouths of our great rivers, and on a smaller scale wher- 

 ever there is running water. Every stream, where it runs into 



Fig. 4. Sketch of Carboniferous strata at Kinghorn, in Fife, showing stratified beds 

 (limestone and shales) surmounted by an unstratified mass of trap. (Original.) 



a lake or into the sea, carries with it a burden of mud, sand, 

 and rounded pebbles, derived from the waste of the rocks 

 which form its bed and banks. When these materials cease 

 to be impelled by the force of the moving water, they sink to 

 the bottom, the heaviest pebbles, of course, sinking first, the 

 smaller pebbles and sand next, and the finest mud last. Ulti- 

 mately, therefore, as might have been inferred upon theoretical 

 grounds, and as is proved by practical experience, every lake 

 becomes a receptacle for a series of stratified rocks produced 

 by the streams flowing into it. These deposits may vary in 

 different parts of the lake, according as one stream brought 

 down one kind of material and another stream contributed 

 another material ; but in all cases the materials will bear ample 

 evidence that they were produced, sorted, and deposited by 

 running water. The finer beds of clay or sand will all be 

 arranged in thicker or thinner layers or laminae; and if there 

 are any beds of pebbles these will all be rounded or smooth, 

 just like the water-worn pebbles of any brook-course. In all 

 probability, also, we should find in some of the beds the re- 



