PALEOZOIC STRATIGRAPHY OF ROCKY MOUNTAINS 387 



SUMMARY OF RESULTS ON SPECIAL PROBLEMS OF 

 INVESTIGATION 



The following progress has been made toward the solution of 

 the four special problems noted in the foreword of this thesis: 



1. The Age of the " Jefferson dolomite" in the Livingston, Yellow- 

 stone National Park, and Absaroka quadrangles. — It has been shown 

 beyond doubt that the Ordovician Bighorn dolomite is present, and 

 characteristically developed, throughout the Absaroka Range, as 

 far north as Livingston Peak in Montana, and in Yellowstone 

 Park. It was included in the " Jefferson dolomite" of Hague, 

 Iddings, and Weed. It is followed disconformably by the true 

 Jefferson dolomite (Devonian), much of which was erroneously 

 included by earlier writers under the name "Three Forks forma- 

 tion." 



2. Middle Paleozoic disconformities . — A well-marked discon- 

 formity between the Lower (Trenton) and Upper (Richmond) 

 divisions of the Bighorn dolomite has been discovered in the Ab- 

 saroka Range. In northwestern Wyoming and southwestern 

 Montana the existence of disconformities at the base of the Big- 

 horn dolomite and at the base of the Jefferson dolomite has been 

 established. Much evidence has been gathered which points 

 toward the existence of disconformities at at least one horizon within 

 the Jefferson dolomite, and at the base of the Mississippian system. 



3. Correlation of Upper Cambrian and Ordovician formations in 

 Wyoming with those in Utah. — The Upper and Lower divisions of 

 the Fish Haven dolomite in northern Utah have been shown to cor- 

 respond in lithologic character to the Upper and Lower divisions, 

 respectively, of the Bighorn dolomite; and there is evidence of a 

 disconformity between the two divisions of the Fish Haven dolo- 

 mite, as well as between those of the Bighorn. Several members 

 of the Gallatin formation of Wyoming and Montana have been 

 tentatively correlated on lithologic grounds with members of the 

 St. Charles formation (Upper Cambrian) in northern Utah, and 

 the main flat-pebble conglomerate zone at the top of the Gallatin 

 is tentatively correlated with a member of similar character in 

 Utah which includes the top of the St. Charles formation and the 

 lower part of the Garden City (Beekmantown) formation. 



