1896. | NEW YORK ACADEMY OF SCIENCES. 255 
and those to the southeast could not be made out. It has been 
supposed by some geologists that the Brown’s Park group sad- 
dled across this divide and extended far to the southeast, but 
the different lithological character of the beds there exposed, as 
well as their resemblance to the Green river shales, seems to in- 
validate such a theory. 
Lithological Characters.—The lithological characteristics of 
the Brown’s Park are exceedingly peculiar and are entirely dif- 
ferent from those of any other tertiary in the region. The most 
characteristic strata are composed of a very soft, friable, silicious. 
silt, everywhere thinly bedded and throughout highly calcareous. 
They differ entirely from those of the Bridger group to the north 
of the mountains and the Uintah to the south, in containing: 
comparatively little clay and being everywhere very soft. The 
Bridger is characterized by a grayish or greenish tinge and the 
Uintah by a prevailing brownish-red color, whilst the Brown’s 
Park is always white. The most important difference, however, 
is in the texture. 
All the Eocene formations in the Green River Basin contain, 
besides their softer strata, seams of a hard compact sandstone 
of either a deep green, brown or yellow color. These seams 
never appear in any part of the Brown’s Park beds. The latter 
are everywhere the same, soft, friable mass which crumbles 
easily in the fingers and offers almost no resistance to erosion. 
For.so soft a formation, indeed, the beds are eroded surprisingly 
little, and one is tempted to wonder, on entering the park, how 
beds of such a nature could have withstood the degrading forces 
of nature for so long a time. Beds of conglomerate also occur, 
but these are confined to the edges of the valley, and since they 
are composed almost wholly of quartzite pebbles were obviously 
derived from the surrounding cliffs of Weber quartzite. 
Geological Age.—In regard to the geological age of the beds 
great difference of opinion has prevailed. King,in studying 
them, did not venture to assign them to any age. He remarks :* 
“The area enclosed between Vermilion Bluffs, Brown’s Peak, 
the Escalante Hills and Snake River is one in which the rela- 
tions of the Tertiary are involved in much obscurity. It is a 
region which has suffered extensive faults and extraordinary 
erosion and is for the most part largely covered by deep accu- 
mulations of soil. It is certain that at some point in Vermilion 
Bluffs the Green River strata occupy the surface, and we are 
unable to observe any break, from Vermilion Bluffs southeast- 
ward into Brown’s Park. The rocks in Brown Park are also in 
great measure covered by local accumulations of soil. Through- 
* U. S. Geological Exploration of the Fortieth Parallel, page 384. 
