"Wi THE NEW EVOLUTION T^^ 



ocean across the plains of Europe and of western 

 Asia. 



Soils are formed from the disintegration of the 

 rocks. Rocks are continually breaking up and being 

 washed away as mud or sand or gravel. In this way 

 there is formed the basic food of the plants which sup- 

 port the butterflies. 



Besides this, the muds and sands and gravels de- 

 posited in water are continually being reformed and 

 consolidated into the so-called sedimentary rocks. 

 Once in a while a butterfly gets stuck in mud and 

 covered up. This mud may later turn to rock. When 

 this happens we have a record of the sort of butterflies 

 that existed at the time when that rock was mud. It 

 is quite unusual to find butterflies as fossils in the 

 rocks, though a fair number have been found and 

 studied. These all belong to that far distant period 

 known as the Miocene and lived many millions of 

 years ago. In spite of their very great antiquity, 

 they differ very little from the kinds we know today. 

 Most of their living representatives, however, are 

 found in different regions. Thus in Colorado we find 

 a type now confined to Africa, and in Germany we find 

 other types which today live only in America. 



Most caterpillars are able to subsist only on a very 

 limited number of different kinds of plants which are 

 closely related to each other in their chemical compo- 

 sition. Thus the cabbage butterfly feeds only on cab- 

 bages and a few closely related plants, and on nas- 

 turtiums. Some enormous groups of butterflies feed 

 only on a single type of plant, as the so-called Aristo- 



