100 IOWA ACADEMY OP SCIENCE 



phenomenon, but is a characteristic of desert regions generally. On 

 account of the excessive dryness of the atmosphere there is practically 

 no chemical decomposition of the rocks to destroy stony and metallic 

 substances. There is little vegetation in which the larger meteoritie 

 fragments are, after striking the surface of the earth, lost to view. Ex- 

 tensive deflation continually keeps the immediate surface of the ground 

 singularly free of the lighter soil-materials, leaving the pebbles and 

 larger rock-fragments always exposed to sky. The coarser rock-debris is 

 often so plentiful that large areas are sometimes covered by veritable 

 pebble-pavements, or rock-mosaics. 



From the desert regions of the globe it is believed will be derived' 

 our chief information concerning meteoritie materials and through them 

 will be opened up an entirely new field of geologic inquiry. 



