448 A. Hague — Age of the Igneous Rocks 



ton has been able to determine a distinct Livingston flora higher 

 than the Laramie, but far more closely allied to a Cretaceous 

 than a Tertiary flora. The importance of the Livingston for- 

 mation in the geological history of the region can hardly be 

 over-estimated, from the fact already pointed out that it is the 

 earliest occurrence of an accumulation, either wholly or in 

 part, of volcanic material following the uplift of the Paleozoic 

 and Mesozoic beds. 



To the east and north of the Livingston formation, but 

 farther removed from the mountains, occurs a still later series 

 of beds made up of the disintegrated sediments of the earlier 

 rocks, including those of the Livingston formation. Apparently 

 they are identical in age with similar deposits found near the 

 junction of the Missouri and Yellowstone rivers, where they 

 in all probability lie upon the Laramie sandstones without the 

 intervention of any beds referable to the Livingston formation ; 

 at least, the latter have not as yet been recognized in this 

 locality. These beds along the Missouri and Yellowstone 

 rivers have long been designated as the Fort Union formation, 

 and have also been of special interest on account of their 

 varied fossil flora, first carefully described by the late Prof. J. 

 S. Newberry. This Fort Union flora is now generally regarded 

 as of Eocene age. 



Returning to the immediate region of the Yellowstone 

 Park, the Laramie sandstones are found at a number of locali- 

 ties, but neither the Livingston nor Fort Union beds are ex- 

 posed, and if ever deposited, have been removed by erosion 

 or buried beneath later igneous outflows. Subsequent to the 

 post-Laramie movement and after a very considerable erosion 

 of the uplifted sandstones, volcanic action broke out with 

 great energy in the Park country. From numerous centers of 

 eruption lavas were thrown out, submerging broad areas of 

 country. Volcanoes of great size surrounded the Park on the 

 east, north, and northwest. The Absaroka Range was built up 

 by the pouring forth of vast accumulations of volcanic 

 ejectamenta, burying the greater part of the earlier range be- 

 neath many thousands of feet of accumulated lavas. These 

 volcanoes followed the lines of orographic movement which 

 took place at the close of the Laramie, along what are now the 

 Absaroka, Snowy, and Gallatin ranges. To-day, this ancient 

 center of eruption lies in the interior of the continent just 

 eastward of the continental watershed which separates the 

 waters of the Atlantic from those of the Pacific, but at the 

 time this vast body of lavas was ejected, they built up a re- 

 markable chain of coast volcanoes along the western shore-line 

 of a gradually retreating ocean. 



