288 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



decay; the individual organisms lost their identity and melted away 

 into a jellylike ooze, which finally became so charged with the toxic 

 products of decay that it became intolerable even to bacteria. When 

 decay finally ceased, the ooze became an excellent preservative, 

 protecting from decay the dehcate plants and animals that it acci- 

 dentally entombed. As the organic ooze or gel was covered by suc- 

 cessive layers and finally by thousands of feet of sediment it was 

 compressed and gradually hardened into a dense substance resembUng 

 hard rubber. Geologists have examined this material under the 

 microscope by grinding small pieces so thin as to be readily translucent. 

 These thin plates of rock, suitably mounted on glass slides, show not 

 only finely preserved microorganisms but in addition an odd assort- 

 ment of wreckage, including the eyes of tiny insects, spatula te scales 

 from mosquitoes' wings, and an abundance of pollen grains. When 

 this hardened organic substance is heated it yields a distillate of crude 

 oil from wliich may be obtained gasoline, fuel oil, and related products. 

 Hence this substance derived from the former residents of the ancient 

 lake is known as "oil shale". So plentiful were the microorganisms 

 and so long did Lake Uinta persist that its deposits now contain locked 

 up the equivalent of more than 70 biUion barrels of crude oU waiting 

 to supply the Nation's needs when the supply of petroleum from wells 

 becomes inadequate. 



Lake Uinta was blessed in its declining years by a return to con- 

 ditions more nearly like those that attended its youth and middle 

 hfe. Refresliing rain heartened the forest to make another stand, 

 and the gradually expanding lake finally purged itself by overflow. 

 Plants of the kinds that fared badly during the protracted drought 

 gradually spread down from the hills and resumed their former habi- 

 tats. But as the streams swelled and expanded the lake in this final 

 stage, they brought with them an unwonted burden of waste from the 

 land — waste that had accumulated during the dry epoch. Thus it 

 came about that the lake was commonly turbid and could not provide, 

 as formerly, the optimum environment for an immense population. 



Moreover, the prime motivating force that brought Lake Uinta 

 into existence and that made possible its long life was beginning to 

 grow feeble. This force had been one of great magnitude, for it was 

 this that had warped the crust of the earth gradually downward 

 into the great basin-shaped depression which the lake occupied. 

 And now that this force was weakening the streams were able to 

 bring sand and silt into the lake a little more rapidly than the down- 

 warping could make room for it. Hence the water became more and 

 more shallow, and stream-laid deposits pushed ever farther and farther 

 out into the basin until there remained only a vast allu\4al plain 

 dotted with swamps and small ponds. The streams that had so long 

 paid tribute to Lake Uinta finally overwhelmed it and brought its 

 rule to an end. 



