26 ANIMALS OF THE PAST 



durability to the dead fishes that rotted in their 

 midst while yet they were only soft mud. 

 For just as a plaster cast boiled in oil becomes 

 thereby denser and more durable, so the oily 

 and other matter coming from decomposing 

 fish operated on the surrounding sand or mud 

 so as to make it more compact." 



It may not be easy to explain how it came 

 to pass that fishes dwelling in salt water, as 

 these undoubtedly did, were thus deposited in 

 great numbers, but we may now and then see 

 how deposits of fresh-water fishes may have 

 been formed. When rivers flowing through a 

 stretch of level country are swollen during the 

 spring floods, they overflow their banks, often 

 carrying along large numbers of fishes. As the 

 water subsides these may be caught in shallow 

 pools that soon dry up, leaving the fishes to 

 perish, and every year the Illinois game asso- 

 ciation rescues from the " back waters " quan- 

 tities of bass that would otherwise be lost. 

 Mr. F. S. Webster has recorded an instance 

 that came under his observation in Texas, 

 where thousands of gar pikes, trapped in a lake 

 formed by an overflow of the Rio Grande, had 



