ANCIENT AMERICAN LAKE— BRADLEY 287 



highest stage the water could not reach the outlet. Thereafter Lake 

 Uinta fluctuated greatly in size with the changing seasons and with 

 every change in the weather, for a lake that has no outlet and loses 

 by evaporation as much as it receives is extremely responsive to slight 

 variations in atmospheric conditions. As the water level varied, it 

 alternately flooded and left bare wide expanses of mud. Upon these 

 wet mud flats scores of fish were stranded and flopped until they 

 stiffened in the sun. Insects, dazzled by the reflected glare from the 

 wet mud, alighted only to have their wings and feet caught in the 

 drying surface film. Wlien the water level rose again, perhaps only 

 by reason of an onshore wind that pushed a thin sheet of water far 

 up over the nearly level bottom, both fish and insects were sealed 

 beneath a new layer of mud and so were preserved and made part 

 of the enduring record. 



As the lake retreated from its former shores it concentrated into 

 smaller compass the community of Uving things that had formerly 

 occupied a more spacious domain. The water was proportionately 

 enriched in dissolved foodstuffs, and the density of the population 

 increased manyfold. But conditions gradually became so congested 

 that many forms were unable to survive. Their place, however, 

 was immediately taken by a host of other organisms better fitted to 

 endure the foul environment. Indeed, after thousands of years of 

 slow dwindling Lake Uinta finally became, at its lowest ebb, a truly 

 horrid thing — a great festering abscess breathing its stench into the 

 shimmering summer heat. The water became bitter with salt, and 

 the decaying organic material in the shallowest places seethed with 

 fly maggots as they fed upon it. How abundant those maggots were 

 is plainly told by the fact that layer after layer of them was buried, 

 and today their overlapping flattened bodies make continuous paper- 

 like layers in the thinly laminated rock that was once the lake-bottom 

 mud. 



This lowest stage in the history of Lake Uinta indicates that the 

 climate had changed from fairly humid to arid. The lake repeatedly 

 deposited salt crystals along its shores and in the wet mud, but never 

 were its waters so concentrated that continuous beds of salt were laid 

 down. As shown by the annual layers the salt crystals formed only, 

 at intervals of about 50 years, which indicates that the water level 

 even then rose and fell tlirough a considerable range as the rates of 

 supply and evaporation varied. 



While Lake Uinta had no outlet and its level was prevailingly low 

 the organisms Uved in so great profusion that their remains accumu- 

 lated on the botton almost to the exclusion of anything else. But 

 that this material endured long enough to be covered and so preserved 

 means that it won a race with a host of bacteria and other scavenging 

 hordes eager to destroy it. In that race, however, it suffered partial 



