THE VOICE OF THE DESERT ^^ 



This tale is one it is well to bear in mind when discussing 

 either geology or evolution. Even the most confident scien- 

 tists admit that they can't "be so precise as all that." In 

 fact they much prefer to talk about the relative age of 

 either rocks or fossils rather than to assign dates, and of 

 course amateurs have even better reason to be cautious. 

 But it is impossible to talk about cuckoos which turned 

 into road runners and plants which lost their leaves with- 

 out beginning to wonder when they did it. 



How long ago did the road runner colonize the desert 

 and the cactus begin to live there? How long, for that 

 matter, has there been a desert in this region for them to 

 colonize? None of these questions can be answered as 

 definitely as students of rocks, or plants, or animals would 

 like to answer them, but they are not totally unanswerable 

 either. And we might as well start with the desert itself. 



Many parts of the earth have been desert-like at many 

 diflPerent periods. During at least part of Paleozoic times 

 (and that means hundreds of milHons of years ago ) much 

 of New York and Pennsylvania, for example, was a desert, 

 though there were certainly no road runners or cacti there 

 because that was a long long time before there were any 

 birds or any flowering plants of any kind. And the region 

 around New York City was to be buried under the ice at 

 least twice between then and now. 



Similarly, the Southwest also has had its ups and downs, 

 literally as well as figuratively. About the time when New 

 York and Pennsylvania were desert, spreading seas were 

 lapping about the region of Tucson, as sedimentaiy rocks 

 in what are now the Santa Rita and the Tucson Mountains 

 show. Later deposits, formed in other parts of Ailzona, 

 indicate that highly arid conditions prevailed there then. 



