cvi GENERAL SUMMARY OF SCIENTIFIC AND 



underlying Rock Springs group, which is cretaceous. The 

 strata from which Lesquereux obtained tertiary plants are 

 above this stratigraphical break, by which they are separated 

 from adjacent beds holding cretaceous mollusks. Thus a 

 more careful stratigraphical study has served to harmonize 

 the apparently conflicting evidence of paleontology. The re- 

 mains of the Dinosaurs of Black Butte are, however, accom- 

 panied by tertiary mollusks and plants. Record, 1874, p, 

 lxx. 



Beneath the mesozoic rocks, which include Jurassic and tri- 

 assic strata, are immense thicknesses of paleozoic rocks, in- 

 cluding Carboniferous, Devonian, Silurian, and Cambrian, the 

 whole series, from the top of the tertiary to the paleozoic base, 

 having, according to the estimate of Major Powell, a thickness 

 of about 60,000 feet. Beneath all these is a series of crystal- 

 line schists, of which about 5000 feet have been measured. 

 The crystalline strata of this region, according to this ob- 

 server, are every where of great and unknown age. Record, 

 1873, p. xlvii. 



Professor Marsh has discussed the cenozoic formations of 

 the West, and pointed out the existence of several great ba- 

 sins corresponding to fresh- water lakes of former periods, 

 which are now filled with deposits whose organic remains 

 enable us to assign them to different divisions of tertiary 

 time. The great Green River basin, lying between the Rocky 

 Mountains and the Wahsatch range, has the Uintah Mount- 

 ains on the south and the Wind River Mountains on the 

 north. Its nearly horizontal strata, with a total thickness of 

 6000 feet, rest unconformably upon the lignitic or cretaceous 

 coal-bearing strata (often highly inclined), and have yield- 

 ed the remains of not less than 150 species of eocene age. 

 This region remained dry land during the miocene time, per- 

 haps much longer, but was afterward submerged, and has 

 suffered great erosion. A still larger lake existed in eocene 

 time to the south of the Uintah Mountains, and at a much 

 lower level than the last. South of the Black Hills is a great 

 miocene area, the White River Lake basin, extending from 

 the Rocky Mountains to the 99th meridian, and from the 

 40th to the 44th parallel. Its strata, which consist of fine 

 materials, have a thickness of about 300 feet, and rest like 

 the preceding on the cretaceous. This area constitutes the 



