EARLY MESOZOIC FORMATIONS. 616 



the distribution of pebbles containing Jurassic fossils afford strong evi- 

 dence that the stream by which the gravels were laid down fiowed'frorn 

 the vicinity of Haskell peak northwardly across Genesee valley and the 

 northern arm of Indian valley to the Mountain meadows. 



There are five formations well exposed on mount Jura. These are the 

 Hinchman tuff, Bicknell sandstone. .Mormon sandstone. Thompson lime- 

 stone and Hardgrave sandstone. They all contain an abundance of 

 fossils, which Professor Hyatt regards as undoubtedly Jurassic. The 

 Hinchman tuff is a greenish or gray sandrock composed in many places 

 of lapilli. The Bicknell sandstone is light gray or bluish gray and 

 sometimes tufaceous above. Its areal relation to the Hinchman tuff has 

 not been satisfactorily determined. They appear to grade into each 

 other, and yet they can be separated both on stratigraphic and paleon- 

 tologic grounds. The Hinchman tuff from both points of view is sup- 

 posed to be the younger. Both formations are well exposed in Hinch- 

 man ravine. As may he seen in Professor Hyatt's paper* they are 

 certainly younger than the other three Jurassic formations and belong 

 to the upper Jura. 



The Mormon sandstone is a line grained, compact, gray fossiliferous 

 sandstone containing several small beds of conglomerate. It is best ex- 

 posed on the spurs of mount Jura above Donnerwirth's, at an elevation 

 of about 4,400 feet. According to Professor Hyatt its fauna belongs to 

 the middle Jura. 



The Thompson limestone is gray above and red and impure below. 

 Near Thompson's it is burned for lime, but its best exposure is between 

 Thompson's and the summit of mount Jura, at an elevation of about 

 l,7<>(> feet. Its position everywhere appears to clearly indicate that it 

 lies between the Mormon and I [ardgrave sandstones. According to Pro- 

 fessor Hyatt, its fossils tend to show that it may be younger than the 

 Mormon sandston 



The I [ardgrave sandstone is the red rock of Mormon canyon from which 

 Brewerand King collected fossils in 1863. Accordingto Professor Hyatt 

 this is the oldesl formation of the Jurassic system in tin' Taylorville 

 region, and should he classed as upper Trias. 



The Foreman beds are well exposed on the grade of the Lucky S 

 mine road. They contain slates and sandstone-:, besides several l>ed> of 

 conglomerate. Near Foreman's Mr. Curtice, in L890. collected from the 

 slates a few plant remains. Mr. E.G. Paul has since added Largely to 



l liia volun 



tit' I that all the limesti among the metamorphic rocks of th< Sii Nevndu 



■ Carboniferous age (U. S irv. Bull. no. 33, p. 21), bul ii is now known thai Jurassie, 



Triusaic and Silurian, as well a- Carboniferous, limesto ir in thai region, 



